Optical disk thickness discriminating apparatus

ABSTRACT

An optical disk apparatus comprising a device for moving a focal point of a light beam for reproducing information recorded on an information face of a disk, in the direction perpendicular to the information face; a device for detecting a reflected light from the disk; and a device for discriminating whether the disk set in the apparatus is a disk having a thick base substrate or a disk having a thin base substrate. In this apparatus, a maximum value AS1L max  of an output signal from the reflected light detecting device and a maximum value ENV max  of an amplitude of an information reproducing signal are detected while driving the focal point moving device so that the focal point passes through the information face, and the discriminating device discriminates whether the disk set in the apparatus is a disk having a thick base substrate or a disk having a thin base substrate, on the basis of the ratio of ENV max  to AS1L max . Therefore, it is possible to discriminate between a DVD having a thin base substrate and a CD having a thick base substrate.

FIELD OF THE INVENTION

The present invention relates to an optical disk apparatus thatreproduces different kinds of disks, such as a compact disk and adigital video disk.

BACKGROUND OF THE INVENTION

There is an optical disk apparatus in which a light beam emitted from alaser is focused on a rotating disk to reproduce signals recorded in thedisk.

FIG. 25 is an enlarged view of a part of a typical compact disk(hereinafter referred to as CD). In the figure, reference numeral 1designates a base substrate of the CD, numeral 2 designates aninformation surface, and numeral 3 designates a series of pits on theinformation surface. These pits 3 provide a spiral track. The pitch ofthe spiral track is 1.6 μm. Aluminum is vapor-deposited on theinformation surface 2 as a reflecting film. The rear surface of thedisk, opposite the information surface 2, is irradiated with a lightbeam. When information recorded on the track is reproduced, focusing isperformed so that a focal point of the light beam is always positionedon the information surface 2 where the Al reflecting film is present,and tracking is performed so that the focal point of the light beam ispositioned on the track. The diameter of the disk is about 120 mm, andthe thickness of the base substrate 1 is 1.2 mm. The wavelength of thelight beam is 780 nm.

In recent years, disks with high recording density, for example, adigital video disk (hereinafter referred to as DVD) in which digitalimage data are recorded, have been proposed. Hereinafter, a DVD will bedescribed as an example of a high recording density disk. However, thepresent invention is not restricted to a DVD.

The recording density of the DVD is about five times as high as that ofthe CD. In order to achieve this recording density, the track pitch isreduced to 0.74 μm and the track recording density (number of data onthe track per a unit length) is increased. With the increase in therecording density, the wavelength of the light beam is reduced to 650nm. In order to reliably reproduce information recorded in the disk evenwhen the disk is inclined, the thickness of a base substrate of the diskis 0.6 mm, that is, thinner than that of the CD. The diameter of the DVDis approximately equal to that of the CD. Hereinafter, this DVD iscalled a single-layer DVD.

Besides the single-layer DVD mentioned above, there is also adouble-layer DVD as shown in FIG. 26. In FIG. 26, reference numeral 4designates a first layer, numeral 5 designates a second layer, numeral 6designates an intermediate layer, and numeral 10 designates a basesubstrate of the DVD. The DVD is irradiated with a light beam at therear surface of the base substrate 10. Like the single-layer DVD, thefirst layer 4 wherein information is recorded is 0.6 mm distant from therear surface of the base substrate 10. A reflecting film comprising Auor the like is employed as the first layer 4, and the reflectivity isreduced to about 35%. So, a part of the light beam passes through thefirst layer 4. This first layer serves as a first information surface.The second layer 5 is located on the first layer 4 with the 40 μm thickintermediate layer 6 between them. The light beam passing through thefirst layer 4 is reflected by the second layer 5 and travels through theintermediate layer 6, the first layer 4, and the base substrate 10. Thissecond layer serves as a second information surface. Thereby,information recorded in the first layer 4 and the second layer 5 can bereproduced. The second layer 5 comprises aluminum or the like, and thereflectivity is about 90%. The recording capacity of this double-layerDVD is about twice as large as that of the single-layer DVD. In thisdouble-layer DVD, when information recorded in the first informationsurface 4 is reproduced, focusing is performed on the first informationsurface 4. When information recorded in the second information surface 5is reproduced, after the focal point is moved from the first informationsurface 4 to the second information surface 5, focusing is performed onthe second information surface 5.

When a CD and a DVD are reproduced using an optical disk apparatus, theapparatus is provided with an optical system for reproducing the CD andan optical system for reproducing the DVD because the CD and the DVDhave different base material thicknesses, and the optical systems areswitched according to a disk set in the apparatus. In order to identifywhether the disk set in the apparatus is a CD or a DVD, a cartridgecontaining the disk has a hole for discrimination.

However, when the disk is not contained in a cartridge, it is impossibleto identify the disk using a cartridge. If the optical system for theDVD is used for the CD, information is not correctly reproduced becauseof the difference in base material thicknesses between the CD and theDVD.

Meanwhile, there is a disk called CD-R which is a recordable opticaldisk of write once read many type. When the CD-R, which employs the sameoptical system for the CD, is set in the optical disk apparatus, if theoptical system for the DVD is selected by mistake, information recordedin the CD-R is sometimes destroyed. This destruction is attributed tothe fact that the CD-R usually employs, for a recording film, an organiccoloring material that highly absorbs light having a wavelength of 650nm and, therefore, the recording film is easily destroyed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical diskapparatus that can discriminate between a CD and a DVD even when thesedisks are not contained in cartridges.

Another object of the present invention is to provide an optical diskapparatus that can discriminate between a CD-R and a DVD withoutdestroying an information surface of the CD-R when the CD-R is set inthe apparatus by mistake.

Other objects and advantages of the invention will become apparent fromthe detailed description that follows. The detailed description andspecific embodiments described are provided only for illustration sincevarious modifications within the scope of the invention will be apparentto those of skill in the art from the detailed description.

According to a first aspect of the present invention, there is providedan optical disk apparatus comprising means for moving a focal point of alight beam for reproducing information recorded on an information faceof a disk, in the direction perpendicular to the information face; meansfor detecting a reflected light from the disk; and means fordiscriminating whether the disk set in the apparatus is a disk having athick base substrate or a disk having a thin base substrate. In thisapparatus, a maximum value AS1L_(max) of an output signal from thereflected light detecting means and a maximum value ENV_(max) of anamplitude of an information reproducing signal are detected whiledriving the focal point moving means so that the focal point passesthrough the information face, and the discriminating means discriminateswhether the disk set in the apparatus is a disk having a thick basesubstrate or a disk having a thin base substrate on the basis of theratio of ENV_(max) to AS1L_(max). Therefore, it is possible todiscriminate between a DVD having a thin base substrate and a CD havinga thick base substrate.

According to a second aspect of the present invention, there is providedan optical disk apparatus comprising means for moving a focal point of alight beam for reproducing information recorded on an information faceof a disk, in the direction perpendicular to the information face; meansfor detecting a reflected light from the disk; a signal detecting meansfor detecting a prescribed frequency component from an output signalfrom the reflected light detecting means; and means for discriminatingwhether the disk set in the apparatus is a disk having a high trackrecording density or a disk having a low track recording density. Inthis apparatus, the discriminating means discriminates whether the diskset in the apparatus is a disk having a high track recording density ora disk having a low track recording density on the basis of an outputsignal from the signal detecting means when the focal point moving meansis driven so that the focal point passes through the information face.Therefore, it is possible to discriminate between a disk having a hightrack recording density and a disk having a low track recording density.

According to a third aspect of the present invention, there is providedan optical disk apparatus comprising means for moving a focal point of alight beam for reproducing information recorded on an information faceof a disk, in the direction perpendicular to the information face; meansfor detecting a reflected light from the disk; means for digitizing anoutput signal from the reflected light detecting means; means formeasuring a high level period or a low level period of time for anoutput signal from the digitizing means; and means for discriminatingwhether the disk set in the apparatus is a disk having a high trackrecording density or a disk having a low track recording density. Inthis apparatus, the discriminating means discriminates whether the diskset in the apparatus is a disk having a high track recording density ora disk having a low track recording density on the basis of a signaloutput from the period measuring means when the focal point moving meansis driven so that the focal point passes through the information face.Therefore, it is possible to discriminate between a disk having a hightrack recording density and a disk having a low track recording density.

According to a fourth aspect of the present invention, there is providedan optical disk apparatus comprising means for moving a focal point of alight beam for reproducing information recorded on an information faceof a disk, in the direction perpendicular to the information face; meansfor detecting a reflected light from the disk; and means fordiscriminating the disk set in the apparatus as a disk employing anorganic coloring material for a recording film when a signal output fromthe reflected light detecting means when the focal point moving means isdriven so that the focal point passes through the information face islower than a prescribed level. Therefore, it is possible to discriminatea CD-R in a relatively simple structure.

According to a fifth aspect of the present invention, theabove-mentioned apparatus further comprises a focus error signaldetector detecting a focus error signal that shows a focused state ofthe light beam irradiating the information face of the disk on the basisof the output signal from the reflected light detecting means, and thediscriminating means discriminates the disk set in the apparatus as adisk employing an organic coloring material for a recording film when anamplitude of the focus error signal is lower than a prescribed level.Therefore, it is possible to discriminate a CD-R in a relatively simplestructure.

According to a sixth aspect of the present invention, in theabove-mentioned apparatus, the discrimination of the disk employing anorganic coloring material is performed with a light beam having anintensity lower than the intensity of the light beam for reproducing theinformation. Therefore, even when the disk set in the apparatus is aCDR, information recorded in the CD-R is not destroyed when the disk isdiscriminated.

According to a seventh aspect of the present invention, there isprovided an optical disk apparatus comprising means for moving a focalpoint of a light beam for reproducing information recorded on aninformation face of a disk, in the direction perpendicular to theinformation face; means for detecting a reflected light from the disk;and means for discriminating whether the disk set in the apparatus is adisk having one information face or a disk having two information faces.In this apparatus, the discriminating means discriminates the disk setin the apparatus as a disk having two information faces when a signaloutput from the reflected light detecting means when the focal pointmoving means is driven so that the focal point passes through theinformation face is lower than a prescribed level. Therefore, thediscrimination between a single-layer DVD and a double-layer DVD can beperformed using the maximum value of the ENV signal, in a relativelysimple structure.

According to an eighth aspect of the present invention, theabove-mentioned apparatus further comprises a focus error signaldetector detecting a focus error signal that shows a focused state ofthe light beam irradiating the information face of the disk on the basisof an output signal from the reflected light detecting means, and thediscriminating means discriminates the disk set in the apparatus as adisk having two information faces when an amplitude of the focus errorsignal is lower than a prescribed level. Therefore, it is possible todiscriminate between a single-layer DVD and a double-layer DVD.

According to a ninth aspect of the present invention, there is providedan optical disk apparatus comprising means for moving a focal point of alight beam for reproducing information recorded on an information faceof a disk, in the direction perpendicular to the information face; meansfor detecting a reflected light from the disk; and means fordiscriminating whether the disk set in the apparatus is a disk having athick base substrate or a disk having a thin base substrate on the basisof a maximum value of an amplitude of an information reproducing signaloutput from the reflected light detecting means when the focal pointmoving means is driven so that the focal point passes through theinformation face. Therefore, the discrimination between a DVD having athin base substrate and a CD having a thick base substrate can beperformed in a relatively simple structure.

According to a tenth aspect of the present invention, in theabove-mentioned apparatus, the information recorded in the disk isreproduced using an optical system for a disk having a thin basesubstrate. Therefore, when a disk having a thin base substrate is set inthe apparatus, the time interval before the reproduction of informationis reduced.

According to an eleventh aspect of the present invention, in theabove-mentioned apparatus, the moving speed of the focal point isreduced by controlling the focal point moving means when the output fromthe reflected light detecting means exceeds a prescribed level.Therefore, level changes of an AS1L signal, an ENV signal, and an FEsignal become gentle, and maximum values of amplitudes of these signalsare accurately detected, whereby the reliability of the diskdiscrimination is improved.

According to a twelfth aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk; a focus error detecting meansfor detecting a focused state of a light beam irradiating theinformation face, on the basis of an output signal from the reflectedlight detecting means; means for controlling focusing so that thefocused state of the light beam becomes a desired state, on the basis ofan output signal from the focus error detecting means; and means forgenerating a timing signal for driving the focusing control means on thebasis of an output signal from the focus error detecting means. In thisapparatus, the focal point moving means is driven so that the focalpoints go away from the disk, and the focusing control means is operatedin response to the timing signal. When no information is reproduced, thefocusing control means is immobilized, and the focal point moving meansis driven so that the focal points approach the disk, and the focusingcontrol means is operated in response to the timing signal. Therefore,even though the apparatus is not provided with a disk discriminatingmeans, the focusing control can be performed with focal points suitablefor the disk having a thick base substrate and the disk having a thinbase substrate, respectively. In addition, when a disk having a thinbase substrate is set in the apparatus, the rise time of the apparatuscan be reduced.

According to a thirteenth aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk; a focus error detecting meansfor detecting a focused state of a light beam irradiating theinformation face on the basis of an output signal from the reflectedlight detecting means; means for controlling focusing so that thefocused state of the light beam becomes a desired state on the basis ofan output signal from the focus error detecting means; and means forgenerating a timing signal for driving the focusing control means on thebasis of an output signal from the focus error detecting means. In thisapparatus, the focal point moving means is driven so that the focalpoints approach the disk, and the focusing control means is operated inresponse to the timing signal. When no information is reproduced, thefocusing control means is immobilized, and the focal point moving meansis driven so that the focal points go away from the disk, and thefocusing control means is operated in response to the timing signal.Therefore, even though the apparatus is not provided with a diskdiscriminating means, focusing control can be performed with focalpoints suitable for the disk having a thick base substrate and the diskhaving a thin base substrate, respectively. In addition, when a diskhaving a thick base substrate is set in the apparatus, the rise time ofthe apparatus can be reduced.

According to a fourteenth aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,this apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk; a focus error detecting meansfor detecting a focused state of a light beam irradiating theinformation face on the basis of an output signal from the reflectedlight detecting means; means for controlling focusing so that thefocused state of the light beam becomes a desired state on the basis ofan output signal from the focus error detecting means; means forgenerating a timing signal for driving the focusing control means on thebasis of an output signal from the focus error detecting means; andmeans for discriminating whether the disk set in the apparatus is a diskhaving a thick base substrate or a disk having a thin base substrate. Inthis apparatus, when the disk set in the apparatus is discriminated as adisk having a thick base substrate, the focal point moving means isdriven so that the focal points approach the disk, and the focusingcontrol means is operated in response to the timing signal. Therefore,when a disk having a thick base substrate is set in the apparatus, thefocusing control can be performed with a focal point suitable for thedisk, and the rise time of the apparatus can be reduced.

According to a fifteenth aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk; a focus error detecting meansfor detecting a focused state of a light beam irradiating theinformation face on the basis of an output signal from the reflectedlight detecting means; means for controlling focusing so that thefocused state of the light beam becomes a desired state on the basis ofan output signal from the focus error detecting means; means forgenerating a timing signal for driving the focusing control means on thebasis of an output signal from the focus error detecting means; andmeans for discriminating whether the disk set in the apparatus is a diskhaving a thick base substrate or a disk having a thin base substrate.When the disk set in the apparatus is discriminated as a disk having athin base substrate, the focal point moving means is driven so that thefocal points go away from the disk, and the focusing control means isoperated in response to the timing signal. Therefore, when a disk havinga thin base substrate is set in the apparatus, the focusing control canbe performed with a focal point suitable for the disk, and the rise timeof the apparatus can be reduced.

According to a sixteenth aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means from moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk; a focus error detecting meansfor detecting a focused state of a light beam irradiating theinformation face, on the basis of an output signal from the reflectedlight detecting means; means for controlling focusing so that thefocused state of the light beam becomes a desired state on the basis ofan output signal from the focus error detecting means; means forgenerating a timing signal for driving the focusing control means on thebasis of an output signal from the focus error detecting means; andmeans for discriminating whether the disk set in the apparatus is a diskhaving a thick base substrate or a disk having a thin base substrate.When the disk set in the apparatus is discriminated as a disk having athick base substrate, the focal point moving means is driven so that thefocal points approach the disk, and the focusing control means isoperated in response to the timing signal. When the disk set in theapparatus is discriminated as a disk having a thin base substrate, thefocal point moving means is driven so that the focal points go away fromthe disk, and the focusing control means is operated in response to thetiming signal. Therefore, the focusing control can be performed withfocal points suitable for the disk having a thick base substrate and thedisk having a thin base substrate, respectively. In addition, the risetime of the apparatus can be reduced in both cases where a disk having athick base substrate is set and where a disk having a thin basesubstrate is set.

According to a seventeenth aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk, having a first lightresponsive region that receives a center portion of the reflected lightand a second light responsive region that receives a peripheral portionof the reflected light; and means for discriminating whether the diskset in the apparatus is a disk having a thick base substrate or a diskhaving a thin base substrate, on the basis of signals detected by thefirst and second light responsive regions when the focal point movingmeans is driven so that the first and second focal points pass throughthe information face. Therefore, the discrimination between a diskhaving a thick base substrate and a disk having a thin base substratecan be performed.

According to an eighteenth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means detects that a focalpoint of a light beam suitable for the disk is near the information facefrom the level of an information reproducing signal detected by thereflected light detecting means, and then discriminates whether the diskset in the apparatus is a disk having a thick base substrate or a diskhaving a thin base substrate on the basis of the signals detected by thefirst and second light responsive regions. Therefore, the discriminationof the disk set in the apparatus is accurately performed.

According to an nineteenth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means detects that a focalpoint of a light beam suitable for the disk is near the information faceon the basis of the ratio of a low frequency signal level of the outputsignal from the reflected light detecting means to the informationreproducing signal level. Therefore, the discrimination of the disk canbe performed accurately even when the reflectivity of the disk varies.

According to a twentieth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means comprises means fordividing an amplitude of an information reproducing signal by a lowfrequency signal level of an output signal from the reflected lightdetecting means; and means for measuring an amount of light AS1Lpreceived by the first light responsive region, an amount of light AS2Lpreceived by the second light responsive region, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the divisionattains a maximum value while driving the focal point moving means sothat the first and second focal points pass through the informationface. The discriminating means discriminates whether the disk set in theapparatus is a disk having a thick base substrate or a disk having athin base substrate on the basis of the ratio of AS1Lp×ENVp to AS2Lp.Therefore, the precision in the discrimination of the disk is improved.

According to a twenty-first aspect of the present invention, in theabove-mentioned apparatus, the discriminating means comprises means foradding an output signal from the first light responsive region to anoutput signal from the second light responsive region; means fordividing an amplitude of an information reproducing signal by a lowfrequency signal level of an output signal from the reflected lightdetecting means; and means for measuring a maximum value ASL_(max)obtained by the adding means and measuring an amount of light AS1Lpreceived by the first light responsive region, an amount of light AS2Lpreceived by the second light responsive region, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the dividingmeans attains a maximum value while driving the focal point moving meansso that the first and second focal points pass through the informationface. The discriminating means discriminates whether the disk set in theapparatus is a disk having a thick base substrate or a disk having athin base substrate on the basis of the ratio of AS1Lp×ENVp toAS2Lp×ASL_(max). Therefore, the discrimination of the disk can beperformed accurately even when the reflectivity of the disk varies.

According to a twenty-second aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; first andsecond light detecting means for detecting a reflected light from thedisk, the second light detecting means receiving a larger portion of thereflected light than the first light detecting means; and means fordiscriminating whether the disk set in the apparatus is a disk having athick base substrate or a disk having a think base substrate on thebasis of signals detected by the first and second light detecting meanswhen the focal point moving means is driven so that the first and secondfocal points pass through the information face. Therefore, thediscrimination between a disk having a thick base substrate and a diskhaving a thin base substrate can be performed.

According to a twenty-third aspect of the present invention, in theabove-mentioned apparatus, the discriminating means detects that a focalpoint of a light beam suitable for the disk is near the information facefrom the level of information reproducing signals detected by the firstand second light detecting means, and then discriminates whether thedisk set in the apparatus is a disk having a thick base substrate or adisk having a thin base substrate on the basis of signals detected bythe first and second light receiving means. Therefore, thediscrimination of the disk can be performed accurately.

According to a twenty-fourth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means detects that a focalpoint of a light beam suitable for the disk is near the information faceon the basis of the ratio of a low frequency signal level in the outputsignals from the first and second light detecting means to theinformation reproducing signal level. Therefore, the discrimination ofthe disk can be performed accurately even when the reflectivity of thedisk varies.

According to a twenty-fifth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means comprises means fordividing an amplitude of an information reproducing signal by a lowfrequency signal level of output signals from the first and second lightdetecting means; and means for measuring an amount of light AS1Lpreceived by the first light detecting means, an amount of light AS2Lpreceived by the second light detecting means, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the divisionattains a maximum value while driving the focal point moving means sothat the first and second focal points pass through the informationface. The discriminating means discriminates whether the disk set in theapparatus is a disk having a thick base substrate or a disk having athin base substrate on the basis of the ratio of AS1Lp×ENVp to AS2Lp.Therefore, the precision in the discrimination of the disk is improved.

According to a twenty-sixth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means comprises means foradding an output signal from the first light detecting means to anoutput signal from the second light detecting means; means for dividingan amplitude of an information reproducing signal by a low frequencysignal level of output signals from the first and second light detectingmeans; and means for measuring a maximum value ASL_(max) obtained by theadding means and measuring an amount of light AS1Lp received by thefirst light detecting means, an amount of light AS2Lp received by thesecond light detecting means, and an amplitude ENVp of the informationreproducing signal when a value obtained by the dividing means attains amaximum value while driving the focal point moving means so that thefirst and second focal points pass through the information face. Thediscriminating means discriminates whether the disk set in the apparatusis a disk having a thick base substrate or a disk having a thin basesubstrate on the basis of the ratio of AS1Lp×ENVp to AS2Lp×ASL_(max).Therefore, the discrimination of the disk can be performed accuratelyeven when the reflectivity of the disk varies.

According to a twenty-seventh aspect of the present invention, there isprovided an optical disk apparatus for reproducing both a disk havingone information face and a disk having two information faces byirradiating the disk with a focused light beam, the apparatus comprisingmeans for moving a focal point of the light beam in the directionperpendicular to the information face; means for detecting a reflectedlight from the disk, having a first light responsive region thatreceives a center portion of the reflected light and a second lightresponsive region that receives a peripheral portion of the reflectedlight; and means for discriminating whether the disk set in theapparatus is a disk having one information face or a disk having twoinformation faces on the basis of signals detected by the first andsecond light responsive regions when the focal point moving means isdriven so that the focal point passes through the information face.Therefore, the discrimination between a disk having one information faceand a disk having two information faces can be performed.

According to a twenty-eighth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means detects that thefocal point of the light beam is near the information face from thelevel of an information reproducing signal detected by the reflectedlight detecting means, and then discriminates whether the disk set inthe apparatus is a disk having one information face or a disk having twoinformation faces on the basis of the signals detected by the first andsecond light responsive regions. Therefore, the discrimination of thedisk can be performed accurately.

According to a twenty-ninth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means detects that thefocal point of the light-beam is near the information face on the basisof the ratio of a low frequency signal level of the output signal fromthe reflected light detecting means to the information reproducingsignal level. Therefore, the discrimination of the disk can be performedaccurately even when the reflectivity of the disk varies.

According to a thirtieth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means comprises means fordividing an amplitude of an information reproducing signal by a lowfrequency signal level of an output signal from the reflected lightdetecting means; and means for measuring an amount of light AS1Lpreceived by the first light responsive region, an amount of light AS2Lpreceived by the second light responsive region, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the divisionattains a maximum value while driving the focal point moving means sothat the focal point passes through the information face. Thediscriminating means discriminates whether the disk set in the apparatusis a disk having one information face or a disk having two informationfaces on the basis of the ratio of AS1Lp×ENVp to AS2Lp. Therefore, theprecision in the discrimination of the disk is improved.

According to a thirty-first aspect of the present invention, in theabove-mentioned apparatus, the discriminating means comprises means foradding an output signal from the first light responsive region to anoutput signal from the second light responsive region; means fordividing an amplitude of an information reproducing signal by a lowfrequency signal level of an output signal from the reflected lightdetecting means; and means for measuring a maximum value ASL_(max)obtained by the adding means and measuring an amount of light AS1Lpreceived by the first light responsive region, an amount of light AS2Lpreceived by the second light responsive region, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the dividingmeans attains a maximum value while driving the focal point moving meansso that the focal point passes through the information face. Thediscriminating means discriminates whether the disk set in the apparatusis a disk having one information face or a disk having two informationfaces on the basis of the ratio of AS1Lp×ENVp to AS2Lp×ASL_(max).Therefore, the discrimination of the disk can be performed accuratelyeven when the reflectivity of the disk varies.

According to a thirty-second aspect of the present invention there isprovided an optical disk apparatus for reproducing both a disk havingone information face and a disk having two information faces byirradiating the disk with a focused light beam, the apparatus comprisingmeans for moving a focal point in the direction perpendicular to theinformation face; first and second light detecting means for detecting areflected light from the disk, the second light detecting meansreceiving a larger portion of the reflected light than the first lightdetecting means; and means for discriminating whether the disk set inthe apparatus is a disk having one information face or a disk having twoinformation faces on the basis of signals detected by the first andsecond light detecting means when the focal point moving means is drivenso that the focal point passes through the information face. Therefore,the discrimination between a disk having one information face and a diskhaving two information faces can be performed.

According to a thirty-third aspect of the present invention, in theabove-mentioned apparatus, the discriminating means detects that thefocal point of the light beam is near the information face, from thelevel of information reproducing signals detected by the first andsecond light detecting means, and then discriminates whether the diskset in the apparatus is a disk having one information face or a diskhaving two information faces on the basis of signals detected by thefirst and second light receiving means. Therefore, the discrimination ofthe disk can be performed accurately.

According to a thirty-fourth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means detects that thefocal point of the light beam is near the information face on the basisof the ratio of a low frequency signal level in the output signals fromthe first and second light detecting means to the informationreproducing signal level. Therefore, the discrimination of the disk canbe performed accurately even when the reflectivity of the disk varies.

According to a thirty-fifth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means comprises means fordividing an amplitude of an information reproducing signal by a lowfrequency signal level of output signals from the first and second lightdetecting means; and means for measuring an amount of light AS1Lpreceived by the first light detecting means, an amount of light AS2Lpreceived by the second light detecting means, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the divisionattains a maximum value while driving the focal point moving means sothat the focal point passes through the information face. Thediscriminating means discriminates whether the disk set in the apparatusis a disk having one information face or a disk having two informationfaces on the basis of the ratio of AS2Lp×ENVp to AS2Lp. Therefore, theprecision in the discrimination of the disk can be improved.

According to a thirty-sixth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means comprises means foradding an output signal from the first light detecting means to anoutput signal from the second light detecting means; means for dividingan amplitude of an information reproducing signal by a low frequencysignal level of output signals from the first and second light detectingmeans; and means for measuring a maximum value ASL_(max) obtained by theadding means and measuring an amount of light AS1Lp received by thefirst light detecting means, an amount of light AS2Lp received by thesecond light detecting means, and an amplitude ENVp of the informationreproducing signal when a value obtained by the dividing means attains amaximum value while driving the focal point moving means so that thefocal point passes through the information face. The discriminatingmeans discriminates whether the disk set in the apparatus is a diskhaving one information face or a disk having two information faces onthe basis of the ratio of AS1Lp×ENVp to AS2Lp×ASL_(max). Therefore, thediscrimination of the disk can be performed accurately even when thereflectivity of the disk varies.

According to a thirty-seventh aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk; means for discriminatingwhether the disk set in the apparatus is a disk having a thick basesubstrate or a disk having a thin base substrate; and an informationface detecting means for detecting that a focal point of a light beamsuitable for the disk is near the information face, from an outputsignal of the reflected light detecting means, while driving the focalpoint moving means so that the first and second focal points passthrough the information face. In this apparatus, the discriminatingmeans discriminates whether the disk set in the apparatus is a diskhaving a thick base substrate or a disk having a thin base substrate onthe basis of the ratio of a maximum value ASL_(max) of a signal outputfrom the reflected light detecting means to a level ASLp of a signaloutput from the reflected light detecting means when the informationface is detected by the information face detecting means, while drivingthe focal point moving means so that the first and second focal pointspass through the information face. Therefore, the discrimination betweena disk having a thick base substrate and a disk having a thin basesubstrate can be performed.

According to a thirty-eighth aspect of the present invention, in theabove-mentioned apparatus, the information face detecting means detectsthat a focal point of a light beam suitable for the disk is near theinformation face on the basis of the ratio of a low frequency signallevel of an output signal from the reflected light detecting means to aninformation reproducing signal level of the output signal. Therefore,the discrimination of the disk can be performed accurately even when thereflectivity of the disk varies.

According to a thirty-ninth aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk; and means for discriminatingwhether the disk set in the apparatus is a disk having a thick basesubstrate or a disk having a thin base substrate. In this apparatus, amaximum value AS1L_(max) of an output from the reflected light detectingmeans and a maximum value ENV_(max) of an amplitude of an informationreproducing signal are measured while driving the focal point movingmeans so that the first and second focal points pass through theinformation face, and the discriminating means discriminates whether thedisk set in the apparatus is a disk having a thick base substrate or adisk having a thin base substrate on the basis of the ratio of ENV_(max)to AS1L_(max). Therefore, the discrimination between a disk having athick base substrate and a disk having a thin base substrate can beperformed.

According to a fortieth aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk; a focus error detecting meansfor detecting focused state of a light beam irradiating the informationface on the basis of an output signal from the reflected light detectingmeans; means for controlling focusing so that the focused state of thelight beam becomes a desired state on the basis of an output signal fromthe focus error detecting means, the focusing control means including anamplifier having a variable amplification factor and amplifying theoutput signal from the focus error detecting means; and an informationface detecting means for detecting that a focal point of a light beamsuitable for the disk is near the information face, from an outputsignal of the reflected light detecting means. In this apparatus, theamplification factor of the amplifier is set on the basis of an outputvalue from the reflected light detecting means when the information facedetecting means outputs an information face detecting signal, whiledriving the focal point moving means so that the first and second focalpoints pass through the information face. Therefore, even when thereflectivity of the disk varies, the amplitude of the FE signal isconstant, whereby an accurate timing for performing the focusing controlis obtained.

According to a forty-first aspect of the present invention, in theabove-mentioned apparatus, after setting the amplification factor of theamplifier, the focusing control means is operated by detecting that anoutput signal from the amplifier reaches a prescribed value. Therefore,the focusing control is avoided from being performed at a wrong timingdue to noise or the like.

According to a forty-second aspect of the present invention, in theabove-mentioned apparatus, the information face detecting means detectsthat a focal point of a light beam suitable for the disk is near theinformation face on the basis of the ratio of a low frequency signallevel of an output signal from the reflected light detecting means to aninformation reproducing signal level of the output signal. Therefore,even when the reflectivity of the disk varies, the presence of thesuitable focal point in the vicinity of the information face can bedetected at an accurate timing.

According to a forty-third aspect of the present invention, in theabove-mentioned apparatus, the discrimination of the disk set in theapparatus is performed after the focal point passes through theinformation face twice. Therefore, the detection of the reflected lightis accurately performed, whereby the precision in the discrimination ofthe disk is improved.

According to a forty-fourth aspect of the present invention, in theabove-mentioned apparatus, the focal point is slightly moved in thedirection perpendicular to a track on the disk during a period of timewhen the focal point is passed through the information face bycontrolling the focusing control means. Therefore, it is avoided thatthe focal point is always positioned between tracks, whereby theprecision in the discrimination of the disk is improved.

According to a forty-fifth aspect of the present invention, in theabove-mentioned apparatus, the moving speed of the focal point isreduced by controlling the focal point moving means when an output valuefrom the reflected light detecting means exceeds a prescribed value.Therefore, the change of the reflected light amount becomes gentle, andthe signal level is accurately detected, whereby the precision in thediscrimination of the disk is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an optical disk apparatus inaccordance with a first embodiment of the present invention.

FIGS. 2(a)-2(d) are waveforms of an FE signal, an AS1 signal, an AS1Lsignal, and an ENV signal, respectively, and FIG. 2(e) illustrates aposition of a focal point F, according to the first embodiment of theinvention.

FIGS. 3(a)-3(d) are waveforms of ENV signals and AS1L signals in asingle-layer DVD, a double-layer DVD, a CD, and a CD-R, respectively,for explaining a disk discriminating process according to the firstembodiment of the invention.

FIG. 4 is a block diagram illustrating an optical disk apparatus inaccordance with a second embodiment of the present invention.

FIG. 5 is a block diagram illustrating an optical disk apparatus inaccordance with a modification of the second embodiment of theinvention.

FIG. 6 is a block diagram illustrating an optical disk apparatus inaccordance with a third embodiment of the present invention.

FIG. 7 is a schematic diagram illustrating an optical system having twofocal points according to the third embodiment of the invention.

FIGS. 8(a)-8(c) are waveforms of FE signals and ENV signals in asingle-layer DVD, a double-layer DVD, and a CD, respectively, accordingto the third embodiment of the invention.

FIGS. 9(a)-9(d) are waveforms of ENV signals and AS1L signals in asingle-layer DVD, a double-layer DVD, a CD, and a CD-R, respectively,for explaining a disk discriminating process according to the thirdembodiment of the invention.

FIG. 10 is a block diagram illustrating an optical disk apparatus inaccordance with a fourth embodiment of the present invention.

FIG. 11 is an schematic diagram illustrating a photodetector included inthe apparatus according to the fourth embodiment of the invention.

FIG. 12 is a flow chart for explaining the operation of the apparatusaccording to the fourth embodiment of the invention.

FIGS. 13(a)-13(c) are waveforms of FE signals, ENV signals, AS1Lsignals, ASL signals, and ENV/ASL values, in a single-layer DVD, adouble-layer DVD, and a CD, respectively, according to the fourthembodiment of the invention.

FIG. 14 is a flow chart for explaining a disk discriminating processaccording to the fourth embodiment of the invention.

FIG. 15 is a flow chart for explaining a disk discriminating processaccording to the fourth embodiment of the invention.

FIGS. 16(a) and 16(b) are waveforms for explaining a movement of afocusing lens for a DVD and a CD, respectively, according to the fourthembodiment of the invention.

FIG. 17 is a waveform of an FE signal for explaining the operation of anamplifier according to the fourth embodiment of the invention.

FIG. 18 is a block diagram illustrating an optical disk apparatusemploying two photodetectors, according to a modification of the fourthembodiment of the invention.

FIGS. 19(a) and 19(b) are schematic diagrams illustrating thephotodetectors shown in FIG. 18.

FIG. 20 is a block diagram illustrating an optical disk apparatus inaccordance with a fifth embodiment of the present invention.

FIGS. 21(a) and 21(b) are waveforms illustrating a movement of afocusing lens and an FE signal, respectively, and FIGS. 21(c) and 21(d)are block diagrams illustrating a signal processing circuit and a CDinformation reproducing circuit, respectively, according to the fifthembodiment of the invention.

FIGS. 22(a) and 22(b) are waveforms illustrating a movement of afocusing lens and an FE signal, respectively, according to the fifthembodiment of the invention.

FIG. 23 is a diagram for explaining relationships between the Z valueand the disk discrimination according to the third embodiment of theinvention.

FIGS. 24(a) and 24(b) are diagrams illustrating positional relationshipsbetween the information face and focal points F_(DVD) and F_(CD), andreflected beams from the information face to a photodetector,respectively, when ENV/ASL attains a maximum value, according to thefourth embodiment of the invention.

FIG. 25 is a schematic diagram illustrating a conventional CD.

FIG. 26 is a schematic diagram illustrating a typical double-layer DVD.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

FIG. 1 is a block diagram illustrating an optical disk apparatus inaccordance with a first embodiment of the present invention.

The optical disk apparatus according to this first embodiment of theinvention can identify whether a disk set in the apparatus is asingle-layer DVD, a double-layer DVD, a CD, or a CD-R. In FIG. 1, when adisk 100 is put on a tray 149, a microcomputer 147 drives a motor 118 tomove the tray 149 so that the disk 100 is fixed to a rotation axis 102of the motor 101.

Reference numeral 104 designates a transport stage. On the transportstage 104, a 650 nm laser 105, a coupling lens 106, a polarization beamsplitter 107, a 1/4 wavelength plate 108, a totally reflecting mirror109, a photodetector 111, a motor 128, and actuators 112 and 127 arefixed. The transport stage 104 is movable in the radial direction of thedisk 100, and the movement is controlled by a transport motor 103, suchas a linear motor.

A light beam emitted from the laser 105 on the transport stage 104 isconverted to a parallel light beam by the coupling lens 106. Theparallel light beam travels through the polarization beam splitter 107and the 1/4 wavelength plate 108 and is reflected by the totallyreflecting mirror 109. The reflected light is conversed by the focusinglens 110 on an information surface of the disk 100. The focusing lens110 and the actuator 112 are used when a DVD is reproduced. When a CD isreproduced, the focusing lens 110b and the actuator 112 for the DVD arechanged to the focusing lens 126 and the actuator 127 for the CD by themotor 128. Although the CD is reproduced using a 780 nm laser in aconventional apparatus for reproducing the CD only, in the optical diskapparatus shown in FIG. 1 the 650 nm laser 105 is employed and thefocusing lens 126 for the CD is designed with regard to this wavelength(650 nm) and the base material thickness of the CD (1.2 mm).

The light beam reflected by the information surface of the disk 100travels through the focusing lens 110 and is reflected by the totallyreflecting mirror 109. The reflected light travels through the 1/4wavelength plate 108, the polarization beam splitter 107, the detectorlens 113, and the cylindrical lens 116, and irradiates the photodetector111 that is divided into four. The focusing lens 110 is fixed to amoving part of the actuator 112. The actuator 112 is composed of a coilfor focusing, a coil for tracking, a permanent magnet for focusing, anda permanent magnet for tracking (these elements are not shown in thefigure). Therefore, when a voltage is applied to the focusing coil ofthe actuator 112 using a power amplifier 133, a current flows throughthis coil and a magnetic force is applied to this coil from thepermanent magnet for focusing, whereby the focusing lens 110 moves inthe direction perpendicular to the surface of the disk 100. In thefigure, the lens 110 moves up and down. In this way, the focusing lens110 is controlled so that the focal point of the light beam is alwayspositioned on the information surface of the disk 100 in response to afocusing error signal that represents an error between the focal pointof the light beam and the information surface of the disk.

When a voltage is applied to the tracking coil of the actuator 112 usinga power amplifier 136, a current flows through this coil and a magneticforce is applied to this coil from the permanent magnet for tracking,whereby the focusing lens 110 moves in the radial direction of the disk100, i.e., the direction transverse to the track on the disk 100. In thefigure, the lens 110 moves right and left.

The light beam reflected by the disk 100 and applied to thephotodetector 111 is converted to current by the photodetector 111 thatis divided into four and is inputted to I/V converters 114, 115, 119,and 120. Each I/V converter converts the inputted current into a voltagein response to the current level. Voltage signals outputted from the I/Vconverters 114, 115, 119, and 120 are inputted to adders 121, 122, 123,and 124 in such a manner that two of the signals outputted from the I/Vconverters are inputted to each adder. Each adder adds the inputted twosignals. Signals outputted from the adders 121, 122, 123, and 124 areinputted to differential amplifiers 125 and 117 in such a manner thattwo of the signals outputted from the adders are inputted to eachdifferential amplifier. The differential amplifier 117 receives signalsoutputted from the adders 123 and 124 and calculates a differencebetween these signals.

The optical system shown in FIG. 1 constitutes a focusing errordetection system that is generally called an astigmatic method. So, anoutput from the differential amplifier 117 becomes a focusing errorsignal (hereinafter referred to as an FE signal) that represents anerror between the focal point of the light beam 150 and the informationsurface of the disk 100. This FE signal is transmitted through a phasecompensator 130, a switch 131, and an adder 132 to the power amplifier133, and a voltage is applied to the focusing coil (not shown) of theactuator 112 by the power amplifier 133. The phase compensator 130 makesthe focusing control system stable. In this way, the focal point of thelight beam is always positioned on the information surface of the disk100 by moving, in response to the FE signal, the focusing lens 110 orthe focusing lens 126 when the focusing lens 110 is changed to thefocusing lens 126.

The differential amplifier 125 receives signals outputted from theadders 121 and 122 and calculates a difference between these signals.The optical system shown in FIG. 1 constitutes a tracking errordetection system that is generally called a push-pull method. Therefore,an output from the differential amplifier 125 becomes a tracking errorsignal (hereinafter referred to as a TE signal) that represents an errorbetween the focal point of the light beam 150 and the track on the disk100. This TE signal is transmitted through a switch 134 and a phasecompensator 135 to the power amplifier 136, and an output from the poweramplifier 136 is applied to the tracking coil (not shown) of theactuator 112 as a voltage. The phase compensator 135 makes the trackingcontrol system stable. In this way, the focal point of the light beam isalways positioned on the track of the disk 100 by moving the focusinglens 110 or the focusing lens 126 in response to the TE signal.

An output from an adder 148 is a signal obtained by adding all thesignals outputted from the photodetector 111, and this signal shows anamount of totally reflected light from the disk 100. Hereinafter, thissignal is called an AS1 signal. This AS1 signal changes according to thepresence and absence of the pits on the disk. This AS1 signal showingthe amount of totally reflected light is sent to an envelope detector143 and to a signal processing circuit (not shown) for demodulatinginformation.

The envelope detector 143 outputs a signal level of an AC componentproduced by the pits on the disk. Hereinafter, this output signal iscalled an ENV signal. A low pass filter 165 (hereinafter referred to asLPF) eliminates the AC component from the ASI signal, and an AS1 signalpassing through the LPF 165 is called an AS1L signal. The AS1L signal,the ENV signal, and the FE signal are converted to digital signals byA/D (analog to digital) converters 142, 144, and 140, respectively, andare sent to the microcomputer 147.

A description is now given of the operation of the optical diskapparatus shown in FIG. 1.

When the disk 100 is put on the tray 149, the microcomputer 147 drivesthe motor 118 so that the disk 100 is fixed to the rotation axis 102 ofthe motor 101.

Next, the microcomputer 147 sets a prescribed value in a D/A (digital toanalog) converter 145 to drive the transport motor 103 through the poweramplifier 139 so that the transport stage 104 moves toward the innercircumference of the disk 100, and drives the motor 128 to select thefocusing lens 110 and the actuator 112 for the DVD.

Further, the microcomputer 147 rotates the motor 101. The rotating speedof the motor 101 is set at a rotating speed normalized for reproductionof information on an inner circumference of a DVD. When the motor 101reaches the rotating speed, the motor 101 sends an OK signal to aterminal a of the microcomputer 147. Receiving the OK signal, themicrocomputer 147 sends a command through a terminal b to a laserdriving circuit 129 so as to make the laser 105 emit light. Meanwhile,the microcomputer 147 sets a radiant intensity of the laser 105, througha D/A converter 146, in the laser driving circuit 129. This radiantintensity must be sufficiently low so that the information recorded inthe disk 100 is not destroyed when the disk 100 is a CD-R.

Further, the microcomputer 147 sets a prescribed value in a D/Aconverter 141 to drive the focusing lens 110 through the adder 132 andthe power amplifier 133 so that the focusing lens 110 moves oncedownward and then gradually upward, that is, once away from the disk 100and then toward the disk 100. At this time, the switches 131 and 134 areopen so that the focusing coil and tracking coil of the actuator 112 arenot driven in response to the FE signal and the TE signal. Thereafter,the microcomputer 147 receives the FE signal, the AS1L signal, and theENV signal through the A/D converters 140, 142, and 144, respectively,while the focusing lens 110 moves, and the microcomputer 147 identifieswhether the disk 100 set in the apparatus is a single-layer DVD, adouble-layer DVD, a CD, or a CD-R on the basis of the FE signal, theAS1L signal, and the ENV signal.

When the disk 100 is identified as a CD-R, since there is the risk ofdestruction of information recorded on the disk 100, the microcomputer147 drives the motor 118 to move the tray 149 so that the disk 100 isejected from the apparatus. When the disk 100 is identified as a CD, themicrocomputer 147 drives the motor 128 to change the actuator 112 andthe focusing lens 110 to the actuator 127 and the focusing lens 126 forthe CD.

Next, the microcomputer 147 controls the laser driving circuit 129 toset the radiant intensity of the laser 105 at an appropriate value forthe disk 100, i.e., a CD or a DVD. Thereafter, the microcomputer 147sets the output from the D/A converter 141 at zero and closes theswitches 131 and 134 to make loops. Using the loops, the microcomputer147 controls the actuator 112 with outputs from the power amplifiers 133and 136 to perform focusing and tracking, respectively, wherebyinformation recorded on the disk 100 is reproduced.

The discrimination of the disk using the microcomputer 147 is performedonly when a disk 100 is newly fixed to the rotation axis 102 of themotor 101. In the case where reproduction of information in the disk ishalted temporarily and then started again, discrimination of the disk isnot performed. Therefore, the rising time when the reproduction isstarted again can be reduced.

A description is now given of the FE signal, the AS1 signal, the AS1Lsignal, and the ENV signal.

FIGS. 2(a), 2(b), 2(c), and 2(d) show waveforms of the FE signal, theAS1 signal, the AS1L signal, and the ENV signal, respectively, when thefocusing lens 110 gradually moves upward in the case where asingle-layer DVD is set in the optical disk apparatus. FIG. (2e) showsthe position of the focal point F. In these figures, the ordinate showsthe signal level, and the abscissa shows time. The FE signal, the AS1signal, the AS1L signal, and the ENV signal vary when the focal point ofthe light beam irradiating the disk passes through the informationsurface, i.e., the Al reflecting film. The FE signal becomes 0 at thetime t1 when the focal point of the light beam is on the informationsurface of the disk. The waveform of the FE signal, when the focal pointof the light beam passes through the information surface of the disk, isgenerally called a S curve. The AS1 signal gradually increases as thefocal point of the light beam approaches the information surface of thedisk and gradually decreases as the focal point goes away from theinformation surface. In addition, the AS1 signal changes according tothe presence and absence of the pits on the disk. The AS1L signal is asignal obtained by averaging the level changes of the AS1 signal due tothe pits on the disk. The ENV signal is a signal showing the levelchange of the amount of the reflected light due to the presence andabsence of the pits on the disk. The position of the focal point F ofthe light beam shown in FIG. (2e) is determined by the signal leveloutputted from the microcomputer 147 and inputted to the D/A converter141.

As shown in FIG. (2e), the microcomputer 147 moves the focal point F ofthe light beam slowly in the period from t0 to t2 because the slowmovement of the focal point makes the change of the signal level gentle,whereby accurate measurement of the respective signals is possible. Inthe period from t0 to t2, the AS1L signal exceeds a reference value wbecause, in this period, the focal point of the light beam is in thevicinity of the information surface of the disk. Therefore, in theperiod from t0 to t2, the focal point F of the light beam is movedslowly to measure the respective signals accurately, whereby the timerequired for discriminating the disk is reduced.

Next, a method of discriminating the disk using the microcomputer 147 inresponse to the FE signal, the AS1L signal, and the ENV signal will bedescribed.

The microcomputer 147 calculates the maximum values of the FE signal,the AS1L signal, and the ENV signal. FIGS. 3(a), 3(b), 3(c), and 3(d)show waveforms of the ENV signal and the AS1L signal when the focusinglens 110 gradually moves upward, for a single-layer DVD (DVD1), adouble-layer DVD (DVD2), a CD, and a CD-R, respectively. In thesefigures, the ordinate shows the signal level, and the abscissa showstime.

In FIG. 3(a), Kenv and Kas show the maximum values of the ENV signal andthe AS1L signal, respectively, within a period of time where thefocusing lens 110 moves. Likewise, Lenv and Las in FIG. 3(b), Menv andMas in FIG. 3(c), and Nenv and Nas in FIG. 3(d) show the maximum values.

The level of the ENV signal and the level of the AS1L signal attainmaximum values in the single-layer DVD and minimum values in the CD-R.The level of the ENV signal and the level of the AS1L signal in thedouble-layer DVD are lower than those in the single-layer DVD becausethe reflectivity of the first layer of the double-layer DVD (about 35% )is lower than the reflectivity of the single-layer DVD (about 90% ).

Further, the ENV signal level Menv in the CD is lower than the ENVsignal levels Kenv and Lenv in the single-layer DVD and the double-layerDVD because the ENV signal in the CD is measured using the opticalsystem for the DVD.

Furthermore, differences in the ENV signal levels (Menv and Nenv) and inthe AS1L signal levels (Mas and Nas) between the CD and the CD-R areattributed to the fact that the absorptivity of the CD-R for 650 nmlight is higher than that of the CD.

The microcomputer 147 stores Pas that satisfies the relationships,NAS<Pas<Mas, Nas<Pas<Las, and Nas<Pas<Kas, and compares the maximumvalue of the AS1L signal with Pas after the calculation of the maximumvalues of the FE signal, the AS1L signal, and the ENV signal. When themaximum value of the AS1L signal is lower than Pas, the microcomputer147 identifies the disk in the apparatus as a CD-R. In this case, themicrocomputer 147 drives the motor 118 to move the tray 149 so that thedisk 100, i.e., the CD-R, is ejected from the apparatus.

Next, the microcomputer 147 calculates Kenv/Kas, Lenv/Las, Menv/Mas, andNenv/Nas. The object of this division of the maximum value of the ENVsignal by the maximum value of the AS1L signal is to absorb influenceson the maximum value of the ENV signal due to variations in thereflectivity of the disk 100 or in the radiant intensity of the laser105. According to an experiment, this value is about 6 in the DVD(single-layer DVD and the double-layer DVD) and about 2 in the CD.Therefore, when this value is larger than 4, the microcomputer 147identifies the disk set in the apparatus as a DVD. When this value islower than 4, the disk is identified as a CD. However, since the resultof the division changes when the amplification factors of the AS1Lsignal and the ENV signal change, the value for comparison must bechanged according to the amplification factors.

When the disk set in the optical disk apparatus is identified as a CD,the microcomputer 147 drives the motor 128 to change the actuator 112and the focusing lens 110 to the actuator 127 and the focusing lens 126for the CD.

When the disk set in the apparatus is identified as a DVD, themicrocomputer 147, which stores Qenv that satisfies the relationship ofLenv<Qenv<Kenv, compares the measured ENV signal with Qenv. According tothe result of the comparison, the microcomputer 147 performs thediscrimination between a single-layer DVD and a double-layer DVD.

Although the discrimination between a single-layer DVD and adouble-layer DVD is performed using the maximum value of the ENV signalin this first embodiment of the invention, it may be performed using themaximum amplitude of the FE signal or the maximum value of the AS1Lsignal because there is a difference in the amplitude level of the FEsignal or the AS1L signal level between the single-layer DVD and thedouble-layer DVD due to the difference in reflectivities between theseDVDS.

Further, although the discrimination of the CD-R is performed using theAS1L signal level in this first embodiment of the invention, it may beperformed using the FE signal level or the ENV signal level because theFE signal level and the ENV signal level in the CD-R are lower thanthose in the CD due to the difference in absorptivities between the CD-Rand the CD. In this first embodiment of the invention, thediscrimination between a CD and a DVD is performed on the basis of thevalue obtained by dividing the maximum value of the ENV signal by themaximum value of the AS1L signal. According to the experiment, themaximum value of the ENV signal in the double-layer DVD, which ismeasured with the lens for the DVD, is larger than the maximum value ofthe ENV signal in the CD, which becomes small because it is measuredwith the lens for the DVD though it should be measured with the lens forthe CD. So, it is possible to identify whether the disk in the apparatusis a single-layer DVD, a double-layer DVD, a CD, or a CD-R on the basisof the maximum value of the ENV signal. More specifically, thediscrimination between a single-layer DVD and a double-layer DVD isperformed using a difference in the reflectivities, and thediscrimination between a DVD and a CD is performed using a difference indetected output signals caused by that an optimum detection lens for thesubstrate thickness is not used. Further, the discrimination between aCD and a CD-R is performed using a difference in the absorptivities.When the discrimination is performed on the basis of the maximum valueof the ENV signal, since the division is not necessary, the processingof the microcomputer 147 is simplified.

In this first embodiment of the invention, the radiant intensity of thelaser 105 is maintained low so that the information on the disk is notdestroyed when the disk is a CD-R. However, after it is found by thefirst vertical movement of the focusing lens 110 that the disk is not aCD-R, the radiant intensity of the laser 105 may be increased and thefocusing lens 110 is moved again to identify whether the disk is a DVDor a CD. Since the level of the detected signal can be made higher thannoise level by increasing the radiant level of the laser, the precisionin the discrimination is significantly improved.

Although the discrimination of the disk is performed using the opticalsystem for the DVD, it may be performed using the optical system for theCD. In this case, however, since the high-low relationships of the ENVsignal and the FE signal are inverted, the conditions for thediscrimination must be changed.

Further, in this first embodiment of the invention, the focusing lens110 once moves downward and then gradually approaches the disk 100 and,during the approach of the lens 110 to the disk 100, the FE signal, theENV signal, and the AS1L signal are measured. However, these signals maybe measured when the focusing lens 110 gradually moves downward awayfrom the disk 100.

As described above, according to the first embodiment of the presentinvention, the maximum values of the AS1L signal and the ENV signal aremeasured, and the maximum value of the ENV signal is divided by themaximum value of the AS1L signal and, thereafter, the result is comparedwith a predetermined reference value. Therefore, it is possible todiscriminate between a DVD having a thin base substrate and a CD havinga thick base substrate.

Since the maximum value of the AS1L signal is compared with a prescribedreference value, the discrimination of a CD-R is performed with a simplestructure.

Since the discrimination of the disk is performed with a light beamhaving an intensity lower than that for reproducing information, evenwhen the disk set in the apparatus is a CD-R, information recorded inthe CD-R is not destroyed.

Since the maximum value of the ENV signal amplitude is compared with aprescribed reference value, the discrimination between a single-layerDVD and a double-layer DVD is performed with a simple structure.

Since the maximum value of the ENV signal amplitude is compared with aprescribed reference value, the discrimination between the DVD having athin base substrate and the CD having a thick base substrate isperformed with a simple structure.

Since the discrimination of the disk is performed using the opticalsystem for the disk having a thin base substrate, when the disk having athin base substrate is set in the apparatus, the time interval requiredbefore reproduction of information in the disk is reduced.

Since the moving speed of the focusing lens 110 is reduced when thelevel of the AS1L signal exceeds the reference value W, the level changeof the AS1L signal, the ENV signal, and the FE signal becomes gentle.Therefore, the microcomputer 147 can receive accurate maximum values ofthe amplitudes of the AS1L signal, the ENV signal, and the FE signal,whereby the discrimination of the disk is performed with highreliability.

Although the discrimination of the CD-R is performed using the maximumvalue of the AS1L signal in this first embodiment of the invention, itmay be performed using the maximum amplitude of the FE signal becausethe amplitude level of the FE signal in the CD-R is lower than that inthe CD due to a difference in absorptivities between the CD-R and theCD.

Furthermore, although the discrimination between a single-layer DVD anda double-layer DVD is performed using the maximum value of the ENVsignal in this first embodiment of the invention, it may be performedusing the maximum amplitude of the FE signal or the maximum value of theAS1L signal because there is a difference in the amplitude level of theFE signal or the AS1L signal level between the single-layer DVD and thedouble-layer DVD due to a difference in reflectivities between theseDVDs.

Embodiment 2

FIG. 4 is a block diagram illustrating an optical disk apparatus inaccordance with a second embodiment of the present invention. In FIG. 4,the same reference numerals as those shown in FIG. 1 designate the sameor corresponding parts. The optical disk apparatus according to thissecond embodiment of the invention can identify whether a disk set inthe apparatus is a DVD or a CD. However, this apparatus cannot identifywhether the disk is a single-layer DVD or a double-layer DVD.

The optical disk apparatus according to this second embodiment isidentical to the optical disk apparatus according to the firstembodiment except that a band-pass filter 160 and a comparator 161 areincluded. The band-pass filter 160 transmits signals with frequencieswithin certain designated ranges. The comparator 161 outputs a highlevel signal when an input signal level exceeds a prescribed value.Therefore, whether signals within the pass band of the band pass filter160 are recorded in the disk 100 or not can be confirmed by the level ofthe output signal from the comparator 160. The pass band of the bandpass filter 160 is set at about 4 MHz.

A description is given of the operation of the optical disk apparatusaccording to this second embodiment.

When the disk 100 is put on the tray 149, the microcomputer 147 drivesthe motor 118 so that the disk 100 is fixed to the rotation axis 102 ofthe motor 101.

Next, the microcomputer 147 sets a prescribed value in a D/A (digital toanalog) converter 145 to drive the transport motor 103 through the poweramplifier 139 so that the transport stage 104 moves toward the innercircumference of the disk 100, and drives the motor 128 to select thefocusing lens 110 and the actuator 112 for the DVD. Then, themicrocomputer 147 rotates the motor 101. The rotating speed of the motor101 is set at a rotating speed normalized for reproduction ofinformation on an inner circumference of a DVD. Further, themicrocomputer 147 sets a value in the D/A converter 141 to move thefocusing lens 110 once downward and then gradually upward toward thedisk 100. At this time, the switches 131 and 134 are open so that thefocusing coil and tracking coil of the actuator 112 are not driven inresponse to the FE signal and the TE signal. The operation describedabove is similar to the operation according to the first embodiment.

A description is now given of a method for discriminating a diskaccording to this second embodiment.

The maximum frequency of signals recorded in a DVD is about 4 MHz, andthe linear velocity of the DVD is about 3.3 m/s. In a CD, the linearvelocity is about 1.3 m/s, and the maximum frequency of reproducedsignals is about 700 KHz. So, when the CD is rotated with the linearvelocity of the DVD, the maximum frequency is given by 700KHz×(3.27/1.3)=1.8 MHz. Therefore, if the output from the comparator 161becomes high level when the focusing lens moves, it is found that asignal component of 4 MHz is included in the detected signal, and thedisk set in the apparatus is identified as a DVD. The operation afterthe discrimination of the disk is similar to the operation according tothe first embodiment.

In this second embodiment of the invention, the band-pass filter 160that transmits the signal component of 4 MHz is employed, and an outputfrom the band-pass filter 160 is input to the comparator 161 to detectwhether the output from the band-pass filter 160 includes the signalcomponent of 4 MHz or not, whereby the discrimination of the disk 100set in the apparatus is performed. However, the detection of the signalcomponent of 4 MHz may be performed by digitizing the input signal tothe band-pass filter 160 and measuring the high-level or low-levelperiod of the signal. When the disk 100 is a DVD, the high-level orlow-level period is about 125 ns. FIG. 5 shows a block diagram of anoptical disk apparatus in this case.

The apparatus shown in FIG. 5 is different from the apparatus shown inFIG. 4 in that it includes a high-pass filter 700 (hereinafter referredto as HPF) receiving the AS1 signal output from the adder 148, acomparator 701 receiving an output from the HPF 700, a counter 702receiving an output from the comparator 701, and a microcomputer 747receiving an output from the counter 702. The HPF 700 transmits only ahigh frequency component of an input signal. The cut-off frequency ofthe HPF 700 is determined so as to transmit a frequency component ofinformation recorded in the disk 100. Therefore, the frequency componentof the information recorded in the disk 100 is inputted to thecomparator 701. The comparator 701 is a digital circuit that converts aninput signal to a high-level signal or a low-level signal with a zerolevel as a reference. Therefore, an output from the comparator 701 is asignal obtained by digitizing the signal component of the informationrecorded in the disk 100. The counter 702 measures the period of thehigh-level or low-level of the input signal and sends the measured valueto the microcomputer 747. When the measured value inputted to themicrocomputer 747 is near 125 ns, the microcomputer 747 identifies thedisk set in the apparatus as a DVD because 125 ns corresponds to asignal component of 4 MHz. The operation of the microcomputer 747 otherthan the discrimination of the disk using the measured value is similarto the operation of the microcomputer 147.

As described above, in the optical disk apparatus shown in FIG. 4,whether the AS1 signal corresponding to the amount of the reflectedlight from the disk 100 includes a signal component of a prescribedfrequency or not is detected by the band-pass filter 160 and thecomparator 161, whereby discrimination between a DVD having a high trackrecording density and a CD having a low track recording density ispossible.

Furthermore, in the optical disk apparatus shown in FIG. 5, whether theAS1 signal corresponding to the amount of the reflected light from thedisk 100 includes a signal component of a prescribed frequency or not isdetected by the high-pass filter 700, the comparator 701, and thecounter 702, whereby discrimination between a DVD having a high trackrecording density and a CD having a low track recording density ispossible.

Embodiment 3

FIG. 6 is a block diagram illustrating an optical disk apparatus inaccordance with a third embodiment of the present invention. In FIG. 6,the same reference numerals as those shown in FIG. 1 designate the sameor corresponding parts. The apparatus according to this third embodimentis identical to the apparatus according to the first embodiment exceptthat an actuator 172, a focusing lens 170, and a hologram 171 areemployed in place of the actuators 112 and 127 and the focusing lenses110 and 126.

The optical system comprising the actuator 172, the focusing lens 170,and the hologram 171 will be explained with reference to a schematicdiagram shown in FIG. 7. The hologram 171 is located in the center ofthe optical axis of the light beam 150. The light beam 150 travelingthrough the focusing lens 170 forms a focal point for the CD (F_(CD))and a focal point for the DVD (F_(DVD)). The focal point F_(CD) is moredistant from the focusing lens 170 than the focal point F_(DVD). Thedistance between the focal point F_(CD) and the focal point F_(DVD) isabout 300 μm. In addition, the intensity of the focal point F_(DVD) isabout twice as high as the intensity of the focal point F_(CD).

FIG. 6, as in the first embodiment of the invention, when the disk 100is put on the tray 149, the microcomputer 147 drives the motor 118 sothat the disk 100 is fixed to the rotation axis 102 of the motor 101.Next, the microcomputer 147 drives the transport motor 103 through thepower amplifier 139 to move the transport stage 104 toward the innercircumference of the disk 100. Then, the microcomputer 147 rotates themotor 101. The rotating speed of the motor 101 is set at a rotatingspeed normalized for reproduction of information on an innercircumference of a DVD. When the motor 101 reaches the set rotatingspeed, the motor 101 sends an OK signal to the terminal a of themicrocomputer 147. Receiving the OK signal, the microcomputer 147 sets avalue in the D/A converter 141 to move the focusing lens 170 oncedownward and then gradually upward. At this time, the switches 131 and134 are open.

When the focusing lens 170 reaches the uppermost position, themicrocomputer 147 discriminates the disk 100. As the result of thediscrimination, when the disk 100 is identified as a CD-R, themicrocomputer 147 drives the motor 118 to move the tray 149 so that thedisk 100 is ejected from the apparatus. When the disk 100 is identifiedas a CD, the microcomputer 147 again moves the focusing lens 170downward and then gradually upward, and closes the switch 131 at thetiming when the ENV signal exceeds a prescribed level and the FE signalcrosses the zero level for the first time, thereby performing thefocusing control.

The reason why the moving direction of the focusing lens 170 is changedbetween the CD and the DVD when the focusing control is performed willbe described hereinafter.

FIGS. 8(a)-8(c) show waveforms of the FE signal and the ENV signal whenthe focusing lens 170 moves once downward and then gradually upward. Theabscissa shows time. In the optical system producing the two focalpoints F_(CD) and F_(DVD) shown in FIG. 7, the FE signal and the ENVsignal change at the focal points F_(CD) and F_(DVD). In thesingle-layer DVD shown in FIG. 8(a) and the double-layer DVD shown inFIG. 8(b), since the focal point F_(CD) is more distant from thefocusing lens 170 than the focal point F_(DVD) as shown in FIG. 7, boththe FE signal and the ENV signal change at the focal point F_(CD) first(right side in the figure) and then at the focal point F_(DVD) (leftside in the figure). Therefore, when the disk 100 is a DVD, the focusinglens 170 is moved once upward and then gradually downward, and thefocusing control is performed at the time when the FE signal crosses thezero level for the first time (time t12 shown in FIG. 8(a) for thesingle-layer DVD) or the second time (time t13 shown in FIG. 8(b) forthe double-layer DVD). When the disk 100 is a CD, the focusing lens 170is moved once downward and then gradually upward, and the focusingcontrol is performed at the timing when the ENV signal exceeds aprescribed value and the FE signal crosses the zero level for the firsttime (time t11 in FIG. 8(c)). The reason why the ENV signal is taken asa condition for the CD shown in FIG. 8(c) is that the waveform shown bythe dotted line (time t10) appears in the FE signal at the surface ofthe base substrate.

A description is now given of a method of discriminating the disk 100using the microcomputer 147.

The microcomputer 147 receives the FE signal, the AS1L signal, and theENV signal while the focusing lens 170 gradually moves upward, andmeasures the maximum values of these signals.

FIGS. 9(a)-9(d) show waveforms of the ENV signals and the AS1L signalsin the single-layer DVD, the double-layer DVD, the CD, and the CD-R,respectively, when the focusing lens 170 gradually moves upward.

In FIGS. 9(a)-9(d), Senv, Tenv, Uenv, and Venv show the maximum valuesof the ENV signals, and Sas, Tas, Uas, and Vas show the maximum valuesof the AS1L signals, within the period of time during which the focusinglens 170 moves.

The ENV signal and the AS1L signal become high level when the focalpoint F_(CD) and the focal point F_(DVD) are on the information surfaceof the disk, respectively. Among the maximum values of the ENV signals,i.e., Senv, Tenv, Uenv, and Venv, in the single-layer DVD, thedouble-layer DVD, the CD, and the CD-R, respectively, Senv is thehighest value, Tenv is approximately equal to Uenv, and Venv is thesmallest value. Further, among the maximum values of the AS1L signals,i.e., Sas, Tas, Uas, and Vas, in the single-layer DVD, the double-layerDVD, the CD, and the CD-R, respectively, Sas and Uas are large andapproximately equal to each other, Tas is smaller than Uas, and Vas isthe smallest value. The reason why the maximum values Tenv and Tas inthe double-layer DVD are smaller than the maximum values Senv and Sas inthe single-layer DVD is that the reflectivity of the first layer of thedouble-layer DVD is lower than the reflectivity of the single-layer DVD.

The reason why the maximum level of the ENV signal due to the focalpoint F_(CD) in the CD (Uenv) is lower than the maximum level of the ENVsignal due to the focal point F_(DVD) in the single-layer DVD (Senv) isthat the amount of light at the focal point F_(CD) is about 50% of theamount of light at the focal point F_(DVD). In addition, the reason whythe maximum level of the ENV signal due to the focal point F_(DVD) inthe CD (Uenv) is lower than the maximum level of the ENV signal due tothe focal point F_(DVD) in the single-layer DVD (Senv) is that the focalpoint F_(DVD) is designed for a 0.6 mm thick base substrate and,therefore, the light beam is defocused.

The differences in the ENV signals and the AS1L signals between the CDand the CD-R, i.e., the difference between Uenv and Venv and thedifference between Usa and Vas, are caused by the fact that theabsorptivity of the CD-R for light of 650 nm wavelength is larger thanthat of CD.

The microcomputer 147 stores Was, in advance, that satisfies therelationships, Vas<Was<Uas, Vas<Was<Tas, and Vas<Was<Sas, and comparesthe maximum value of the AS1L signal with Was. When the maximum value issmaller than Was, the microcomputer 147 identifies the disk 100 set inthe apparatus as a CD-R. In this case, the microcomputer 147 drives themotor 118 to move the tray 149 so that the disk 100 is ejected from theapparatus.

Then, the microcomputer 147 calculates Senv/Sas, Tenv/Tas, and Uenv/Uas.Senv/Sas is approximately equal to Tenv/Tas. Uenv/Uas is smaller thanSenv/Sas and Tenv/Tas.

The microcomputer 147 stores a prescribed value Z in advance andcompares a value obtained by dividing the maximum value of the ENVsignal by the maximum value of the AS1L signal with the value Z, wherebythe microcomputer 147 identifies whether the disk 100 set in theapparatus is a DVD or a CD.

A description is given of the value Z.

Initially, Senv/Sas, Tenv/Tas, and Uenv/Uas are measured for a standarddisk, and the value Z is determined on the basis of the result of themeasurement. In an apparatus where the intensity of the focal pointF_(DVD)) is about twice as high as the intensity of the focal pointF_(CD), the value Z is about 6 in the single-layer DVD and thedouble-layer DVD and about 2 in the CD. Therefore, Z takes a valuebetween 2 and 6. In order to perform accurate discrimination of the diskeven when the characteristics of the disk vary, Z is set at a value thatsatisfies 6/Z=Z/2. So, Z is about 4. FIG. 23 shows the relationshipbetween the value Z and the disk. When the value obtained by dividingthe maximum value of the ENV signal by the maximum value of the AS1Lsignal is larger than 4, the disk is identified as a DVD. When the valueis smaller than 4, the disk is identified as a CD. However, since theresult of the division varies with a difference in amplification factorsbetween the ENV signal and the AS1L signal, when the amplificationfactors are changed, the value Z must be changed according to theamplification factors. Further, when the ratio of the intensity of thefocal point F_(DVD) to the intensity of the focal point F_(CD) ischanged, the value for the comparison must be changed according to theintensity ratio.

As described above, according to the third embodiment of the presentinvention, the maximum values of the AS1L signal and the ENV signal aremeasured, the maximum value of the ENV signal is divided by the maximumvalue of the AS1L signal, and the result of the division is comparedwith a prescribed reference value. Therefore, in an optical diskapparatus utilizing an optical head having two focal points, i.e., afocal point for reproducing a disk of a thick base substrate and a focalpoint for reproducing a disk of a thin base substrate, it is possible todiscriminate between a DVD having a thin base substrate and a CD havinga thick base substrate.

Further, when the microcomputer 147 identifies the disk 100 set in theapparatus is a CD having a thick base substrate, the microcomputer 147sets a prescribed value in the D/A converter 141 to move the focusinglens 170 toward the disk 100. Meanwhile, the microcomputer 147 detectsthe timing for performing the focusing control and closes the switch 131at this timing, thereby performing the focusing control. Therefore, inthe optical disk apparatus utilizing an optical head having two focalpoints, i.e., a focal point for reproducing a disk of a thick basesubstrate and a focal point for reproducing a disk of a thin basesubstrate, the focusing control can be normally performed for the CD.

Furthermore, when the microcomputer 147 identifies the disk 100 as a DVDhaving a thin base substrate, the microcomputer 147 sets a prescribedvalue in the D/A converter 141 to move the focusing lens 170 downward,i.e., away from the disk 100. Meanwhile, the microcomputer 147 detectsthe timing for performing the focusing control and closes the switch 131at this timing, thereby performing the focusing control. Therefore, inthe optical disk apparatus utilizing an optical head having two focalpoints, i.e., a focal point for reproducing a disk of a thick basesubstrate and a focal point for reproducing a disk of a thin basesubstrate, the focusing control can be normally performed regardless ofthe thickness of the base substrate.

Embodiment 4

FIG. 10 is a block diagram illustrating an optical disk apparatus inaccordance with a fourth embodiment of the present invention. In FIG.10, the same reference numerals as those shown in FIG. 6 designate thesame or corresponding parts. Reference numeral 411 designates aphotodetector, numeral 447 designates a microcomputer, numeral 450designates an I/V converter, numeral 451 designates a low-pass filter,numerals 452 and 461 designate A/D converters, numeral 453 designates avariable amplifier, numerals 454 and 462 designate adders, and numeral455 designates a D/A converter.

The photodetector 411 has a light responsive surface divided into fiveparts. That is, a light responsive surface is added to the photodetector111 according to the third embodiment. FIG. 11 is a schematic diagramshowing the photodetector 411. As shown in FIG. 11, the photodetector411 according to this fourth embodiment has five light responsive partsA, B, C, D, and E whereas the photodetector 111 according to the thirdembodiment has four light responsive parts A, B, C, and D. The lightresponsive parts A, B, C, and D constitute an inner region of thephotodetector 411, and the inner region is about 200 μm along each side.The light responsive part E constitutes an outer region of thephotodetector 411, and the outer region is about 2 mm along each side.

An output from the adder 148, i.e., a signal obtained by adding outputsignals from the light responsive parts A, B, C, and D, is called anAS1L signal hereinafter. Therefore, as in the third embodiment of theinvention, an output from the differential amplifier 117 becomes an FEsignal that shows an error between the focal point of the light beam 150and the information face of the disk 100. In addition, an output fromthe differential amplifier 125 becomes a TE signal that shows an errorbetween the focal point of the light beam 150 and the track on the disk100. An output from the light responsive part E is sent to the I/Vconverter 450. An output from the I/V converter 450 is sent to the adder462 and the LPF 460. An output signal from the adder 462 is a signalobtained by adding output signals from all the light responsive parts ofthe photodetector 411, and this signal is called an ASL signalhereinafter. Likewise, an output signal from the LPF 451 is called anASL signal, an output signal from the I/V converter 450 is called an AS2signal, and an output signal from the LPF 460 is called an AS2L signal.The ASL signal is sent to the A/D converter 461. The microcomputer 447receives an output from the A/D converter 461 and receives the AS2Lsignal through the A/D converter 452. The I/V converter 450 operates inthe same way as the I/V converter 120. Likewise, the LPFs 451 and 460and the A/D converters 461 and 452 operate in the same way as the LPF165 and the A/D converter 142, respectively. The amplifier 453 canchange the amplification factor in response to a command from themicrocomputer 447. The adder 454 and the D/A converter 455 operate inthe same way as the adder 132 and the D/A converter 141, respectively.

The operation of the optical disk apparatus shown in FIG. 10 will bedescribed using a flow chart shown in FIG. 12.

When the disk 100 is put on the tray 149, the microcomputer 447 drivesthe motor 118 to set the disk 100 to the rotation axis 102 of the motor101 (step S1).

Next, the microcomputer 447 drives the transport motor 103 through theD/A converter 145 and the power amplifier 139 to move the transportstage 104 toward the inner circumference of the disk 100 (step S2).Then, the microcomputer 447 rotates the motor 101 (step S3). Therotating speed of the motor 101 is set at a rotating speed normalizedfor reproduction of information on an inner circumference of a DVD.

Further, the microcomputer 447 discriminates the disk 100 to identifywhether the disk 100 is a DVD, a CD, or a CD-R (step S4). A method ofdiscriminating the disk will be described later. The system for thediscrimination is constructed so that the position of the focusing lens170 at the completion of the discriminating process is nearer to thedisk 100 than the position of the focusing lens 170 when the focusingcontrol is normally performed.

A description is given of the operation of the apparatus when the disk100 is identified as a DVD.

The microcomputer 447 sets an amplification factor of the amplifier 453on the basis of a value AS1Lp (p means "peak") that is measured in thediscriminating process (step S5). Next, through the D/A converter 141,the adder 132, and the power amplifier 133, the microcomputer 447 movesthe focusing lens 170 gradually downward. The FE signal detected duringthe downward movement of the lens 170 is amplified by the amplifier 453and A/D converted by the A/D converter 140, and the timing when the FEsignal crosses the zero level for the first time (hereinafter referredto as zero cross timing) is detected on the basis of an output from theA/D converter 140 (step S6). When the zero cross timing is detected, theoutput from the D/A converter 141 is made zero and the switch 131 isclosed, thereby performing the focusing control (step S6). The AS1Lpsignal will be described later.

A description is given of the operation of the apparatus when the disk100 is identified as a CD.

As in the case of the DVD, the microcomputer 447 sets an amplificationfactor of the amplifier 453 on the basis of the value AS1L measured inthe discriminating process (step 7). Further, the microcomputer 447 setsthe rotating speed of the motor 101 at a rotating speed normalized forreproduction of information on an inner circumference of a CD.

Next, the focusing lens 170 is moved once downward (step S8) and thengradually upward, and the timing when the ENV signal output from theenvelope detector 143 exceeds a prescribed level for the first time andthe FE signal crosses the zero level for the first time is detected onthe basis of the output from the A/D converter 140 (step S9). When thezero cross timing is detected, the output from the D/A converter 141 ismade zero and the switch 131 is closed, thereby performing the focusingcontrol (step S9).

The reason why the moving direction of the focusing lens 170 is changedbetween the CD and the DVD is as described for the third embodiment ofthe invention. Therefore, when a DVD is set in the apparatus, since thestep of moving the focusing lens once downward is dispensed with, it ispossible to start the signal reproduction within a short time, comparedto the case where a CD is set in the apparatus. Therefore, when DVDs arefrequently set in the apparatus as compared with CDs, the signalreproduction can be started within a short time on the average.

When the disk 100 is identified as a CD-R, the motor 118 is driven tomove the tray 149 so that the disk 100 is ejected from the apparatus(step S10).

Next, a method of discriminating a disk using the microcomputer 447 willbe described.

FIGS. 13(a)-13(c) show levels of an FE signal, an ENV signal, an AS1Lsignal, and an ASL signal, and an ENV/ASL value which is obtained bydividing the ENV signal level by the AS1L signal level, for asingle-layer DVD, a double-layer DVD, and a CD, respectively.

The ENV signal and the AS1L signal change due to the focal point F_(CD)for the CD and the focal point F_(DVD) for the DVD. In addition, the FEsignal has a level change, generally called an S curve, when the focalpoint F_(CD) (F_(DVD)) passes through the information face of the disk.

According to an experiment, in case of the DVD, ENV/ASL attains amaximum value when the focal point F_(DVD) is on the information face.The reason is as follows. Since the ASL signal is a low frequencycomponent of the light beam reflected by the disk, ENV/ASL shows theratio of modulated amount of the light beam irradiating the disk by thepits on the disk. Therefore, when the focal point suitable for the diskset in the apparatus is on the information face of the disk, informationrecorded in the disk is reproduced with high efficiency. So, in case ofthe DVD, ENV/ASL attains a maximum value when the focal point F_(DVD) ison the information face of the disk. In case of the single-layer DVD,ENV/ASL attains a maximum value at time t31 in the waveform shown inFIG. 13(a). In case of the double-layer DVD, at times t32 and t33 in thewaveform shown in FIG. 13(b) where the focal point F_(DVD) is on thefirst and second information faces of the disk, respectively, ENV/ASLattains a maximum value. In case of the CD, ENV/ASL attains a maximumvalue at time t30 in the waveform shown in FIG. 13(c) where the focalpoint F_(CD) is on the information face of the disk.

Although in this fourth embodiment the ENV signal is obtained from theamount of light ASL received by the light responsive parts A, B, C, D,and E of the photodetector 411, the ENV signal may be obtained from theamount of light-AS1L received by the light responsive parts A, B, C, andD. Further, although ENV is divided with ASL, AS1L may be used in placeof ASL. In this case, under the condition where ENV/ASL attains amaximum value, a value of AS1L/AS2L, which is obtained by dividing theAS1L level by the AS2L level that is obtained by subtracting the AS1Llevel from the ASL level, is larger in the single-layer DVD than in thedouble-layer DVD and the CD. That is, in the single-layer DVD, theintensity of light beam in the center of the photodetector 411 isincreased.

The reason will be described using FIGS. 24(a) and 24(b). FIGS. 24(a)and 24(b) show conditions where ENV/ASL attains a maximum value for asingle-layer DVD, a double-layer DVD, and a CD. More specifically, FIG.24(a) shows the positional relationships between the information face ofthe disk 100 and the focal points F_(DVD) and F_(CD), and FIG. 24(b)shows reflected beams from the information face of the disk 100 to thephotodetector 411.

Initially, the single-layer DVD will be described. In the single-layerDVD, ENV/ASL attains a maximum value when the focal point F_(DVD) is onthe information face. The reflected beam from the information face ofthe disk 100 is narrowed by the detection lens 113 and applied to thephotodetector 411 through the cylindrical lens 116. Therefore, thereflected beam RB_(DVD) of the beam for the DVD (hereinafter referred toas DVD beam) forms a focal point in the center of the photodetector 411.However, since the focal point F_(CD) is not on the information face ofthe disk, the reflected beam RB_(CD) of the beam for the CD (hereinafterreferred to as CD beam) is incident on the entire surface of thephotodetector 411 and irradiates the surface dimly.

Next, the double-layer DVD will be described. In the double-layer DVD,ENV/ASL attains a maximum value when the focal point F_(DVD) is on thefirst information face or the second information face. In the figure,the focal point F_(DVD) is on the first information ace. AS1L/AS2Lobtained when the focal point F_(DVD) is on the first information faceis approximately equal to AS1L/AS2L obtained when the focal pointF_(DVD) is on the second information face.

In the double-layer DVD, the reflected beam RB_(DVD1) of the DVD beamfrom the first information face forms a focal point in the center of thephotodetector 411. The DVD beam and the CD beam traveling through thefirst information face are reflected by the second information face tobe a reflected beam RB_(DVD2) and a reflected beam RB_(CD),respectively, and are incident on the entire surface of thephotodetector 411 because the focal point F_(CD) of the CD beam and thefocal point F_(DVD) of the DVD beam passing through the firstinformation face are not on the information face.

Since the reflectivity at the information face of the single-layer DVDis higher than the reflectivity at the information faces of thedouble-layer DVD, the amount of the inner side light beam incident onthe photodetector 411 in the single-layer DVD (the reflected beamRB_(DVD)) is larger than the amount of the inner side light beamincident on the photodetector 411 in the double-layer DVD (the reflectedbeam RB_(DVD1)). In case of the double-layer DVD, the reflected beamRB_(DVD2) of the DVD beam from the second information face is incidenton the entire surface of the photodetector 411 and the reflected beamRB_(CD1),2 of the CD beam from the first and second information faces isadded to the reflected beam RB_(DVD2). So, the amount of the outer sidelight beam incident on the photodetector 411 in the double-layer DVD islarger than the amount of the outer side light beam incident on thephotodetector 411 in the single-layer DVD (the reflected beam RB_(CD)).Therefore, as described above, AS1L/AS2L is larger in the single-layerDVD than in the double-layer DVD.

Finally, the CD will be described. In the CD, ENV/ASL attains a maximumvalue when the focal point F_(CD) is on the information face of thedisk. Therefore, the reflected beam RB_(CD) of the CD beam forms a focalpoint in the center of the photodetector 411. The reflected lightRB_(DVD) of the DVD beam is incident on the entire surface of thephotodetector 411 because the focal point F_(DVD) is not on theinformation face.

Since the intensity of the focal point F_(DVD) is higher than theintensity of the focal point F_(CD), the amount of the inner side lightbeam incident on the photodetector 411 in the single-layer DVD (thereflected beam RB_(DVD)) is larger than the amount of the inner sidelight beam incident on the photodetector 411 in the CD (the reflectedbeam RB_(CD)). In case of the CD, since the reflected beam RB_(DVD) ofthe DVD beam is incident on the entire surface of the photodetector 411,the amount of the outer side light beam incident on the photodetector411 is larger than the amount of the outer side light beam incident onthe photodetector 411 in the single-layer DVD (the reflected beamRB_(CD)).

Therefore, as described above, AS1L/AS2L is larger in the single-layerDVD than in the CD.

According to the experiment, AS1L/AS2L in the single-layer DVD is about1.5 times as large as those in the double-layer DVD and the CD. Further,the level ENVp of the ENV signal under the condition that ENV/ASLattains a maximum value is higher in the single-layer DVD than in thedouble-layer DVD and the CD. In case of a disk having a standardreflectivity, the maximum value ASL_(max) of ASL is approximately thesame in a single-layer DVD, a double-layer DVD, and a CD.

A description is now given of a method for discriminating a single-layerDVD.

While moving the focusing lens 170 in the direction perpendicular to theinformation face of the disk 100, ENV/ASL is calculated, and AS1Lp,AS2Lp, ASLp, and ENVp at the moment when the ENV/ASL attains a maximumvalue are stored. Meanwhile, the maximum value ASL_(max) of ASL withinthe period of time during which the focusing lens 170 moves is measured.Using these values, a value Y is given by

    Y=(ENVp/ASL.sub.max)×AS1Lp/AS2Lp

The value Y is significantly larger in the single-layer DVD than in thedouble-layer DVD and the CD. According to the experiment, the value Y inthe single-layer DVD is about four times as large as those in thedouble-layer DVD and the CD. Therefore, a value F intermediate the valueY in the single-layer DVD and the value Y in the double-layer DVD or theCD is calculated in advance, and this value F is compared with the valueY, whereby it is identified whether the disk 100 is a single-layer DVDor not. Since ASL_(max) is used, the value Y is not adversely affectedby variations in the reflectivity of the disk.

Although in this fourth embodiment the discrimination is performed usingthe value Y, a value Y2 obtained in the following formula may beemployed for the discrimination in place of the value Y.

    Y2=AS1Lp/AS2Lp

Further, when the variation in the reflectivity of the disk is small, avalue Y3 obtained in the following formula may be employed for thediscrimination.

    Y3=ENVp×AS1Lp/AS2Lp

The optical disk apparatus according to this fourth embodiment canreproduce a single-layer DVD, a double-layer DVD, and a CD. However, inan apparatus for reproducing two disks, a single-layer DVD and a CD, itis possible to discriminate between the single-layer DVD and the CDusing the value Y. That is, discrimination between a disk having a thinbase substrate and a disk having a thick base substrate is possible.

Hereinafter, a method of discriminating between a double-layer DVD and aCD will be described.

While moving the focusing lens 170 in the direction perpendicular to theinformation face of the disk 100, ENV/ASL is calculated, and AS1Lp atthe moment when the ENV/ASL attains a maximum value is measured.Meanwhile, the maximum value ASL_(max) of ASL within the period of timeduring which the focusing lens 170 moves is measured. Using thesevalues, a value Z is given by

    Z=ASLp/ASL.sub.max

The value Z is larger in the double-layer DVD than in the CD. The reasonis as follows. In the double-layer DVD, when the focal point F_(DVD) ison the first information face, the light beam traveling through thefirst information face is reflected by the second information face, andmost of the reflected light is incident on the photodetector 411 becausethe distance between the first information face and the secondinformation face is as short as about 40 μm. The same may be said whenthe focal point F_(DVD) is on the second information face.

Further, in the CD, when the focal point F_(DVD) is on the informationface, the light beam forming the focal point F_(DVD) is reflected at theinformation face, and most of the reflected light is incident on thephotodetector 411. Under this condition, ASL attains a maximum valuebecause the amount of light at the focal point F_(DVD) is larger thanthe amount of light at the focal point F_(CD). Further, when the focalpoint F_(CD) is on the information face, the light beam forming thefocal point F_(DVD) is reflected at the information face and becomes astray light, a part of which is not incident on the photodetector 411,because the distance between the focal point F_(CD) and the focal pointF_(DVD) is as long as about 300 μm. Therefore, the ASL level is reducedas compared with the case where the focal point F_(DVD) is on theinformation face.

According to the experiment, the value Z is about 1 in the double-layerDVD and about 0.5 in the CD. Therefore, when a value G intermediate thevalue Z in the double-layer DVD and the value Z in the CD is calculatedin advance and this value G is compared with the value Z, discriminationbetween a double-layer DVD and a CD is possible.

However, in the single-layer DVD, since the amount of light at the focalpoint F_(DVD) is larger than the amount of light at the focal pointF_(CD), even when a part the reflected light of the light beam formingthe focal point F_(CD) is not incident on the photodetector 411, ASLp isnot adversely affected. Therefore, the value Z is approximately 1.Although, in this fourth embodiment, discrimination between adouble-layer DVD and a CD is performed using the value Z, discriminationbetween a single-layer DVD and a CD is also possible. That is,discrimination between a disk having a thick base substrate and a diskhaving a thin base substrate is possible using the value Z.

The operation of the microcomputer 447 in the above-mentioneddiscriminating process will be described using a flow chart shown inFIGS. 14 and 15.

The microcomputer 447 substitutes L_(max) for a variable FODA (step S11)and sets a value of the variable FODA in the D/A converter 141 (stepS12), whereby the focusing lens 170 moves upward. Here, L_(max)satisfies that both the focal point F_(CD) and the focal point F_(DVD)are positioned above the information surface of the disk. This point inthe flow chart is denoted as point a. Thereafter, the respectivevariables, AS1Lp, AS2Lp, ASLp, ENVp, ASL_(max), and Q_(max) are cleared(step S13). This point in the flow chart is denoted as point b. Afterpoint b, a value obtained by subtracting S from the variable FODA issubstituted for the variable FODA (step S14). Then, the variable FODA isset in the D/A converter (step S15). Here, S is much smaller thanL_(max) and a positive value. Therefore, an output value from the D/Aconverter 141 becomes small and is transmitted through the adder 132 andthe power amplifier 133 to the focusing lens 170, whereby the focusinglens 170 moves slightly downward. In this state, the microcomputer 447calculates ENV/ASL and substitutes this value for the variable Q (stepS18). Then, the microcomputer 447 substitutes AS2L, AS1L, and ENV forthe variables AS2Lp, AS1Lp, and ENVp, respectively (step S19).Thereafter, the microcomputer 447 compares the variable ASL_(max) withASL (step S20). When the variable ASL_(max) is smaller than ASL, themicrocomputer 447 substitutes ASL for the variable ASL_(max) (step S21).

Next, when the variable FODA is larger than L_(min) (NO in step S22),the processing returns to point b. When the variable FODA is smallerthan L_(min) (YES in step S22), the operation proceeds to the next step.This point in the flow chart is denoted as point c. Here, L_(min)satisfies that both the focal point F_(CD) and the focal point F_(DVD)are positioned below the information face of the disk.

During the processing from point a to point c, the focal point F_(CD)and the focal point F_(DVD) pass through the information face of thedisk once. The processing after point c is shown in FIG. 15.

The processing from point c to point d is similar to the processing frompoint b to point c mentioned above except that a value obtained byadding S to the variable FODA is substituted for the variable FODA (stepS11a), step S12 is followed by step S16, and the processing is concludedwhen the variable FODA becomes larger than L_(max) (YES in step S22a).During the processing from point c to point d, the focal point F_(CD)and the focal point F_(DVD) pass through the information face of thedisk once. Therefore, during the processing from point a to point d, thefocal point F_(CD) and the focal point F_(DVD) pass through theinformation face of the disk twice. Thereby, the moment when ENV/ASLattains a maximum value is detected accurately. Further, during theprocessing from point b to point d, the microcomputer 447 outputs a sinewave through the D/A converter 455 toward the adder 454, and the sinewave is applied to the focusing lens 170 through the phase compensator135 and the power amplifier 136, whereby the focusing lens 170 vibratesin the direction perpendicular to the track on the disk. Since thevibration of the focusing lens 170 prevents the focal point from beingalways positioned between the tracks, the information recorded on thetracks is easily reproduced, and an accurate level of the ENV signal ismeasured.

FIGS. 16(a) and 16(b) show variations in the position of the focusinglens 170 during the discrimination of the disk according to theabove-mentioned operation. In the figures, the abscissa shows time, andthe ordinate shows the position of the lens 170. The upward direction ofthe ordinate means that the lens 170 approaches the disk 100. The pointsa, c, and d shown in FIGS. 14 and 15 correspond to points a, c, and dshown in FIG. 16. When the discrimination is concluded, the focusinglens 170 is positioned above. When the disk 100 is a DVD, while movingthe focusing lens 170 gradually downward, the first zero cross point ofthe FE signal is detected to perform the focusing control. When the disk100 is a CD, the focusing lens 170 is moved once downward and thengradually upward and, during the upward movement of the lens 170, thefirst zero cross point of the FE signal is detected to perform thefocusing control.

Therefore, when a DVD is set in the apparatus, reproduction of signalscan be started within a short time, compared to the case where a CD isset in the apparatus.

Next, a description is given of setting an amplification factor of theamplifier 453 on the basis of AS1Lp. The setting of the amplificationfactor is performed to secure an accurate detection of the timing forperforming the focusing control. Initially, the timing for performingthe focusing control will be described with reference to FIG. 17.

FIG. 17 shows an FE signal in a single-layer DVD. The abscissa showstime. As the focusing lens 170 moves downward, the focal point F_(DVD)approaches the information face of the disk. The FE signal is negativeat first. When the focal point F_(DVD) reaches the information face, theFE signal becomes zero and, thereafter, it becomes positive. The timingfor performing the focusing control is shown by point f at which thefocal point F_(DVD) is on the information face. At point f, it isdetected that the FE signal exceeds the comparison level Lc. In order toreduce the delay in the detection, the comparison level Lc must be nearthe zero level Lz. However, since the FE signal includes noise and thelike, it is impossible to make the comparison level Lc zero. Therefore,the comparison level Lc is not the zero level Lz.

By the way, the amplitude of the FE signal decreases with a reduction inthe reflectivity at the information face of the disk or a reduction inthe intensity of the light beam 150. Even though the comparison level Lcis fixed, when the amplitude of the FE signal decreases, the delay inthe detection increases. In the worst case, the amplitude of the FEsignal does not reach the comparison level Lc. In the figure, the FEsignal with reduced amplitude is shown by the dotted line. In this case,the timing for performing the focusing control cannot be detected, sothat the focusing control cannot be performed.

The variation in the reflectivity of the information face of the disk orthe intensity of the light beam 150 appears as a level change of theAS1Lp signal when the focal point is on the information face. That is,the level of the AS1Lp signal reduces with a reduction in thereflectivity of the information face of the disk. So, when theamplification factor of the amplifier 453 is set according to the levelof the AS1Lp signal when the focal point for the disk set in theapparatus, i.e., F_(DVD) or F_(CD), is on the information face, an FEsignal with a constant amplitude can be obtained even though thereflectivity of the information face varies. As a result, the timing forperforming the focusing control can be detected accurately and reliablywithout a reduction in the amplitude of the FE signal as shown by thedotted line in FIG. 17.

Now, an amplitude of the FE signal and a value of AS1Lp in a standardcondition are represented by H and J, respectively. Since ALS1Lp isproportional to the amplitude of the FE signal, when the amplitude ofthe FE signal is reduced to H/2, AS1Lp is reduced to J/2. Since AS1Lp isJ/2, i.e., 50% of that in the standard condition, the microcomputer 447doubles the amplification factor of the amplifier 453. Thereby, theamplitude of the FE signal inputted to the A/D converter 140 becomes H,i.e., the amplitude in the standard condition. As a result, the timingfor performing the focusing control can be detected with highreliability.

According to this fourth embodiment of the invention, in case of theDVD, ENV/ASL attains a maximum value when the focal point F_(DVD) is onthe first information face (single-layer DVD) or when the focal pointF_(DVD) is on the first information face or the second information face(double-layer DVD). In case of the CD, ENV/ASL attains a maximum valuethen the focal point F_(CD) is on the information face. According to theexperiment, ENV/AS1L and ENV/ASL show similar characteristics, so thatENV/AS1L may be used in place of ENV/ASL. Further, although the ENVsignal is detected from the AS signal, it may be detected from the AS1signal.

While in this fourth embodiment of the invention a single photodetector411 having a light responsive surface divided into five parts isemployed, two photodetectors may be employed when the structure of theoptical system is changed. FIG. 18 is a block diagram illustrating anoptical disk apparatus including two photodetectors. In the figure, thesame reference numerals as those shown in FIG. 10 designate the same orcorresponding parts. Reference numeral 111 designates a photodetector,numeral 601 designates a half mirror, and numeral 602 designates aphotodetector. The photodetectors 111 and 602 and the half mirror 601are fixed onto the transport stage 104.

FIGS. 19(a) and 19(b) are schematic diagrams illustrating thephotodetector 111 and the photodetector 602, respectively. As shown inthese figures, the photodetector 111 has four light responsive parts A,B, C, and D corresponding to the light responsive parts A, B, C, and Dof the photodetector 411 shown in FIG. 11, and the photodetector 602 hasa light responsive part (hatched part) corresponding to the lightresponsive part E of the photodetector 411. These photodetectors 111 and602 are fixed so that the center points P and Q are aligned with theoptical axis of incident light.

The light beam traveling through the cylindrical lens 116 is dividedinto two beams by the half mirror 601, and one of the beams is incidenton the photodetector 111 while the other is incident on thephotodetector 602. The photodetector 602 is positioned so that thedistance from the half mirror 601 to the photodetector 602 is equal tothe distance from the half mirror 601 to the photodetector 111.Therefore, input signals to the I/V converters 114, 115, 119, 120, and450 are similar to those in the apparatus shown in FIG. 10. Therefore,the operation of the apparatus shown in FIG. 18 is similar to theoperation of the apparatus shown in FIG. 10. As described above,according to the fourth embodiment of the present invention, in anoptical disk apparatus using an optical head having two focal points,i.e., a focal point for reproducing a disk having a thick base substrateand a focal point for reproducing a disk having a thin base substrate,the photodetector 411 detects the intensity of the reflected light inthe center region and the intensity of the reflected light in theperipheral region. Therefore, it is possible to discriminate between aDVD having a thin base substrate and a CD having a thick base substrateon the basis of the intensity ratio.

Further, since the amount of light incident on the photodetector 411when the ENV signal attains a maximum value is used for thediscrimination of the disk 100, the discrimination is accuratelyperformed.

Likewise, since the amount of light incident on the photodetector 411when a value obtained by dividing the ENV signal by the ASL signalattains a maximum value is used for the discrimination of the disk 100,the discrimination is accurately performed even when the reflectivity ofthe disk 100 varies.

Furthermore, the amount of light AS1Lp incident on the first lightresponsive region of the photodetector 411, the amount of light AS2Lpincident on the second light responsive region of the photodetector 411,and the amplitude ENVp of the information signal are measured, and theratio of AS1Lp×ENVp to AS2Lp is used for the discrimination of the disk100, whereby the accuracy of the discrimination is improved.

Furthermore, the amount of light AS1Lp incident on the first lightresponsive region of the photodetector 411, the amount of light AS2Lpincident on the second light responsive region of the photodetector 411,the amplitude ENVp of the information signal, and ASL_(max) aremeasured, and the ratio of AS1Lp×ENVp to AS2Lp×ASL_(max) is used for thediscrimination of the disk 100, the discrimination is accuratelyperformed even when the reflectivity of the disk 100 varies.

The same effects as mentioned above are attained in the optical diskapparatus shown in FIG. 18 including the two photodetectors 111 and 602.

Furthermore, according to the fourth embodiment of the presentinvention, in an optical disk apparatus using an optical head having twofocal points, i.e., a focal point for reproducing a disk having a thickbase substrate and a focal point for reproducing a disk having a thinbase substrate, the photodetector 411 detects the intensity of thereflected light in the center region and the intensity of the reflectedlight in the peripheral region. Therefore, it is possible todiscriminate between a disk having a single information face and a diskhaving two information faces on the basis of the intensity ratio.

Further, since the amount of light incident on the photodetector 411when the ENV signal attains a maximum value is used for thediscrimination of the disk 100, the discrimination is accuratelyperformed.

Likewise, since the amount of light incident on the photodetector 411when a value obtained by dividing the ENV signal by the ASL signalattains a maximum value is used for the discrimination of the disk 100,the discrimination is accurately performed even when the reflectivity ofthe disk 100 varies.

Furthermore, the amount of light AS1Lp incident on the first lightresponsive region of the photodetector 411, the amount of light AS2Lpincident on the second light responsive region of the photodetector 411,and the amplitude ENVp of the information signal are measured, and theratio of AS1Lp×ENVp to AS2Lp is used for the discrimination of the disk100, whereby the accuracy of the discrimination is improved.

Furthermore, the amount of light AS1Lp incident on the first lightresponsive region of the photodetector 411, the amount of light AS2Lpincident on the second light responsive region of the photodetector 411,the amplitude ENVp of the information signal, and ASL_(max) aremeasured, and the ratio of AS1Lp×ENVp to AS2Lp×ASL_(max) is used for thediscrimination of the disk 100, the discrimination is accuratelyperformed even when the reflectivity of the disk 100 varies.

The same effects as mentioned above are attained in the optical diskapparatus shown in FIG. 18 including the two photodetectors 111 and 602.

Furthermore, according to the fourth embodiment of the presentinvention, in an optical disk apparatus using an optical head having twofocal points, i.e., a focal point for reproducing a disk having a thickbase substrate and a focal point for reproducing a disk having a thinbase substrate, when it is detected from the output of the photodetector411 that a focal point appropriate for the disk 100 set in the apparatusis present in the vicinity of the information face, the amplificationfactor of the variable amplifier 453 that amplifies the focal pointerror signal is changed according to the amount of light AS1Lp.Therefore, even when the reflectivity of the disk 100 varies, theamplitude of the FE signal is constant, whereby an accurate timing forperforming the focusing control is obtained.

Further, after changing the amplification factor of the amplifier 453,focusing control is performed at the timing when the output signal fromthe amplifier 453 reaches a prescribed level. Therefore, it is avoidedthat the focusing control is performed at a wrong timing due to noise orthe like.

Furthermore, since the amount of light incident on the photodetector 411when a value obtained by dividing the ENV signal by the ASL signalattains a maximum value is used for the timing detection, even when thereflectivity of the disk 100 varies, the presence of the appropriatefocal point in the vicinity of the information face can be detected ataccurate timing.

Furthermore, since each of the two focal points, i.e., the focal pointfor reproducing a disk having a thick base substrate and the focal pointfor reproducing a disk having a thin base substrate, passes through theinformation face twice, the amount of reflected light from the disk 100is accurately detected.

Embodiment 5

FIG. 20 is a block diagram illustrating an optical disk apparatus inaccordance with a fifth embodiment of the present invention. In thefigure, the same reference numerals as those shown in FIG. 6 designatethe same or corresponding parts. Reference numeral 500 designates asignal processing circuit, and numeral 547 designates a microcomputer.

The signal processing circuit 500 reproduces information recorded in thedisk 100 according to an output signal AS1 from the adder 148, convertsthe information to digital data, and sends the digital data to themicrocomputer 547. The signal processing circuit 500 can reproduce boththe CD and the DVD. The switching of the operation is commanded by themicrocomputer 547.

The operation of the apparatus shown in FIG. 20 will be described usingwaveforms shown in FIGS. 21(a) and 21(b). The waveform in FIG. 21(a)shows the position of the focusing lens 170, and the waveform in FIG.21(b) shows the FE signal as an output signal from the differentialamplifier 117.

In FIG. 20, when the disk 100 is put on the tray 149, the microcomputer547 drives the motor 118 so that the disk 100 is fixed to the rotationaxis 102 of the motor 101. Next, the microcomputer 547 rotates the motor101. The rotating speed of the motor 101 is set at a rotating speed ofan inner circumference of a CD. The microcomputer 547 sets a value inthe D/A converter 141 to move the focusing lens 170 once downward (t210in FIG. 21(a)). Thereafter, the microcomputer 547 moves the focusinglens 170 gradually upward. At this time, the switches 131 and 134 areopen. Since an output signal from the D/A converter 141 is sent throughthe adder 132 and the power amplifier 133 to the actuator 172, the levelof the output signal from the D/A converter 141 corresponds to theposition of the focusing lens 170.

While moving the focusing lens 170 gradually upward, the switch 131 isclosed at the timing when the ENV signal exceeds a prescribed value andthe FE signal crosses the zero level for the first time, therebyperforming the focusing control. This timing is denoted by t211 in FIG.21(b). As already described for the third embodiment of the invention,when the disk 100 is a CD, this timing for performing the focusingcontrol is the timing when the focal point F_(CD) is on the informationface of the disk. Therefore, the focusing control is performed so thatthe focal point F_(CD) is on the information face of the CD. Then, themicrocomputer 547 closes the switch 134 to perform the tracking control.Further, the microcomputer 547 controls the signal processing circuit500 to select the CD information reproducing circuit 602. Therefore, thesignal processing circuit 500 reproduces information recorded in the CDand sends data to the microcomputer 547. In FIGS. 21(a) and 21(b),waveforms shown by dotted lines appear when the focusing control is notperformed, as described for the third embodiment of the invention.

Furthermore, the signal processing circuit 500 will be described indetail with reference to FIGS. 21(c) and 21(d).

FIG. 21(c) is a block diagram showing the signal processing circuit 500.In FIG. 21(c), a first input terminal 601 is connected to the adder 148and receives the AS1 signal. An output terminal 605 is connected to themicrocomputer 547. A CD information reproducing circuit 602 is a circuitfor reproducing information recorded in a CD. A DVD informationreproducing circuit 603 is a circuit for reproducing informationrecorded in a DVD. A switch 606 selects a signal at terminal a or asignal at terminal b according to a level of control terminal d andsends the signal to terminal c. A second input terminal 604 is connectedto the control terminal d of the switch 606.

FIG. 21(d) is a block diagram illustrating the CD informationreproducing circuit 602. An input terminal 704 receives the AS1 signal.An output terminal 705 is connected to the switch 606. A high-passfilter 700 eliminates a low frequency component. A comparator 701outputs a high level signal when the level of an input signal is higherthan zero, and outputs a low level signal when the level of the inputsignal is lower than zero. A periodic pattern detector 706 detects aperiodic pattern at the top of a frame in a signal format of the CD. Aconverter 702 converts 17-bit input data to 8-bit data. A referencetiming for dividing input data to 17-bit data is based on an outputsignal from the periodic pattern detector 706. This conversion isperformed according to a conversion table based on EFM(eight-to-fourteen modulation) that is a CD system modulation process.In the EFM, 14-bit data within 17-bit data have information, and the14-bit data can take only 256 kinds of values. Therefore, the conversiontable converts 256 kinds of input data to 8-bit data corresponding tothe input data. An output signal from the converter 702 is sent to anerror corrector 703 wherein errors in the CD system are corrected.

Since the focal point F_(CD) is now on the information face of the CD,data corresponding to one of the 256 kinds of data on the conversiontable is inputted to the converter 702. Therefore, the input data arecorrectly converted, whereby information recorded in the disk 100 isreproduced.

A description is given of the operation when the disk 100 is a DVD.Although the disk 100 is a DVD, the timing for performing the focusingcontrol is the timing when the focal point F_(CD) is on the informationface of the disk. Therefore, the focusing control is performed so thatthe focal point F_(CD) is on the information face of the disk. Themicrocomputer 547 closes the switch 134 to perform the tracking control.Further, the microcomputer 547 controls the signal processing circuit500 to select the CD information reproducing circuit 602.

However, since the CD system modulation process is different from amodulation process for the DVD, the data inputted to the converter 702in the signal processing circuit 500 is different from the 256 kinds ofdata on the conversion table. So, the converter 702 does not output dataand, therefore, the error corrector 703 is not operated. In this case,no information is sent to the microcomputer 547.

When the microcomputer 547 knows that no information is sent from thesignal processing circuit 500, it identifies the disk 100 as a DVD.Then, the microcomputer 547 opens the switches 131 and 134 to immobilizethe focusing control system and the tracking control system. Thesubsequent processing will be described using waveforms shown in FIGS.22(a) and 22(b). The waveform in FIG. 22(a) shows the position of thefocusing lens 170, and the waveform in FIG. 22(b) shows the FE signal asan output signal from the differential amplifier 117.

The microcomputer 547 sets the rotating speed of the motor 101 at arotating speed of an inner circumference of a DVD. The microcomputer 547sets a value in the D/A converter 141 to move the focusing lens 170 oncetoward the disk 100 (t310 in FIG. 22(a)). Thereafter, the microcomputer547 moves the focusing lens 170 gradually downward and closes the switch131 at the timing when the FE signal crosses the zero level for thefirst time, thereby performing the focusing control. This timing isdenoted by t311 in FIG. 22 (b). As already described for the thirdembodiment of the invention, when the disk 100 is a DVD, this timing forperforming the focusing control is the timing when the focal pointF_(DVD) is on the information face of the disk. Thereafter, themicrocomputer 547 closes the switch 134 to perform the tracking control.Further, the microcomputer 547 controls the signal processing circuit500 to select the DVD information reproducing circuit 603. Therefore,the signal processing circuit 500 reproduces information recorded in thedisk 100 and sends data to the microcomputer 547. In FIGS. 22(a) and22(b), waveforms shown by dotted lines appear when the focusing controlis not performed, as described for the third embodiment of theinvention.

In this fifth embodiment of the invention, the microcomputer 547 startsthe operation on the assumption that the disk 100 is a CD, it may startthe operation on the assumption that the disk 100 is a DVD. In thiscase, the rotating speed of the motor 101 is set at a rotating speed ofan inner circumference of a DVD. The focusing lens 170 is moved onceupward and then gradually downward, and the focusing control isperformed at the first zero cross timing of the FE signal, and thetracking control is performed. The DVD information reproducing circuit603 is selected in the signal processing circuit 500. When noinformation is reproduced, the disk 100 is identified as a CD, and thefocusing control system and the tracking control system are immobilized.Then, the rotating speed of the motor 101 is set at a rotating speed ofan inner circumference of a CD. The focusing lens 170 is moved oncedownward and then gradually upward, and the focusing control isperformed at the timing when the ENV signal exceeds a prescribed leveland the FE signal crosses the zero level for the first time, and thetracking control is performed. In the signal processing circuit 500, theCD information reproducing circuit 602 is selected.

As described above, according to the fifth embodiment of the invention,in an optical disk apparatus using an optical head having two focalpoints, i.e., a focal point for reproducing a disk having a thick basesubstrate and a focal point for reproducing a disk having a thin basesubstrate, even when the focusing control is performed using aninappropriate focal point, the signal processing circuit 500 detectsthat the focusing control is performed with the inappropriate focalpoint. Therefore, it is possible to try the focusing control again withan appropriate focal point.

What is claimed is:
 1. An optical disk apparatus for reproducinginformation recorded on an information face of a disk set in saidoptical disk apparatus using an optical head having a first focal pointfor reproducing a disk having a thick base substrate and a second focalpoint for reproducing a disk having a thin base substrate, said opticaldisk apparatus comprising:focal point moving means for moving the firstand second focal points in a direction perpendicular to the informationface; reflected light detecting means for detecting a reflected lightfrom the disk, said reflected light detecting means having a first lightresponsive region that receives a center portion of the reflected lightand a second light responsive region that receives a peripheral portionof the reflected light; and discriminating means for discriminatingwhether the disk set in said optical disk apparatus is the disk having athick base substrate or the disk having a thin base substrate on thebasis of signals detected by the first and second light responsiveregions when said focal point moving means is driven so that the firstand second focal points pass through the information face.
 2. Theapparatus of claim 1, wherein said discriminating means detects that afocal point of a light beam, suitable for the disk is near theinformation face on the basis of a level of an information reproducingsignal detected by said reflected light detecting means, and thendiscriminates whether the disk set in said optical disk apparatus is thedisk having the thick base substrate or the disk having the thin basesubstrate on the basis of the signals detected by the first and secondlight responsive regions.
 3. The apparatus of claim 2, wherein saiddiscriminating means detects that the focal point of the light beam,suitable for the disk is near the information face on the basis of aratio of a low frequency signal level of an output signal from saidreflected light detecting means to a level of the informationreproducing signal.
 4. The apparatus of claim 1, wherein saiddiscriminating means comprises:division means for dividing an amplitudeof an information reproducing signal by a low frequency signal level ofan output signal from said reflected light detecting means; and meansfor measuring an amount of light AS1Lp received by the first lightresponsive region, an amount of light AS2Lp received by the second lightresponsive region, and an amplitude ENVp of the information reproducingsignal when a value obtained by said division means attains a maximumvalue while driving said focal point moving means so that the first andsecond focal points pass through the information face; wherein saiddiscriminating means discriminates whether the disk set in said opticaldisk apparatus is the disk having the thick base substrate or the diskhaving a thin base substrate on the basis of a ratio of AS1Lp×ENVp toAS2Lp.
 5. The apparatus of claim 1, wherein said discriminating meanscomprises:adding means for adding an output signal from the first lightresponsive region to an output signal from the second light responsiveregion; dividing means for dividing an amplitude of an informationreproducing signal by a low frequency signal level of an output signalfrom said reflected light detecting means; and means for measuring amaximum value ASL_(max) obtained by said adding means and for measuringan amount of light AS1Lp received by the first light responsive region,an amount of light AS2Lp received by the second light responsive region,and an amplitude ENVp of the information reproducing signal when a valueobtained by said dividing means attains a maximum value while drivingsaid focal point moving means so that the first and second focal pointspass through the information face; wherein said discriminating meansdiscriminates whether the disk set in said optical disk apparatus is thedisk having the thick base substrate or the disk having a thin basesubstrate on the basis of a ratio of AS1Lp×ENVp to AS2Lp×ASL_(max). 6.An optical disk apparatus for reproducing both a disk having oneinformation face and a disk having two information faces by irradiatingthe disks with a focused light beam, said optical disk apparatuscomprising:focal point moving means for moving a focal point of thefocused light beam in a direction perpendicular to the information face;reflected light detecting means for detecting a reflected light from thedisk, said reflected light detecting means having a first lightresponsive region that receives center portion of the reflected lightand a second light responsive region that receives a peripheral portionof the reflected light; and discriminating means for discriminatingwhether the disk set in said optical disk apparatus is the disk havingone information face or the disk having two information faces on thebasis of signals detected by the first and second light responsiveregions when said focal point moving means is driven so that the focalpoint passes through the information face.
 7. The apparatus of claim 6,wherein said discriminating means detects that the focal point of thefocused light beam is near the information face on the basis of a levelof an information reproducing signal detected by said reflected lightdetecting means, and then discriminates whether the disk set in saidoptical disk apparatus is the disk having one information face or thedisk having two information faces on the basis of the signals detectedby the first and second light responsive regions.
 8. The apparatus ofclaim 7, wherein said discriminating means detects that the focal pointof the focused light beam is near the information face on the basis of aratio of a low frequency signal level of an output signal from saidreflected light detecting means to a level of the informationreproducing signal.
 9. The apparatus of claim 6, wherein saiddiscriminating means comprises:division means for dividing an amplitudeof an information reproducing signal by a low frequency signal level ofan output signal from said reflected light detecting means; and meansfor measuring an amount of light AS1Lp received by the first lightresponsive region, an amount of light AS2Lp received by the second lightresponsive region, and an amplitude ENVp of the information reproducingsignal when a value obtained by said division means attains a maximumvalue while driving said focal point moving means so that the focalpoint passes through the information face; wherein said discriminatingmeans discriminates whether the disk set in said optical disk apparatusis the disk having one information face or the disk having twoinformation faces on the basis of a ratio of AS1Lp×ENVp to AS2Lp. 10.The apparatus of claim 6, wherein said discriminating meanscomprises:adding means for adding an output signal from the first lightresponsive region to an output signal from the second light responsiveregion; dividing means for dividing an amplitude of an informationreproducing signal by a low frequency signal level of an output signalfrom said reflected light detecting means; and means for measuring amaximum value ASL_(max) obtained by said adding means and for measuringan amount of light AS1Lp received by the first light responsive region,an amount of light AS2Lp received by the second light responsive region,and an amplitude ENVp of the information reproducing signal when a valueobtained by said dividing means attains a maximum value while drivingsaid focal point moving means so that the focal point passes through theinformation face; wherein said discriminating means discriminateswhether the disk set in said optical disk apparatus is the disk havingone information face or the disk having two information faces on thebasis of a ratio of AS1Lp×ENVp to AS2Lp×ASL_(max).
 11. An optical diskapparatus for reproducing information recorded on an information face ofa disk set in said optical disk apparatus using an optical head having afirst focal point for reproducing a disk having a thick base substrateand a second focal point for reproducing a disk having a thin basesubstrate, said optical disk apparatus comprising:focal point movingmeans for moving the first and second focal points in a directionperpendicular to the information face; reflected light detecting meansfor detecting a reflected light from the disk; a focus error detectingmeans for detecting a focused state of a light beam irradiating theinformation face on the basis of an output signal from said reflectedlight detecting means; focusing control means for controlling a focusingof the light beam so that the focused state of the light beam becomes adesired state on the basis of an output signal from said focus errordetecting means, wherein said focusing control means comprises anamplifier having a variable amplification factor for amplifying theoutput signal from said focus error detecting means; and informationface detecting means for detecting that a focal point of a light beam,suitable for the disk set in said optical disk apparatus, is near theinformation face on the basis of the output signal of said reflectedlight detecting means; wherein the variable amplification factor of saidamplifier is set on the basis of an output value from said reflectedlight detecting means when said information face detecting means outputsan information face detecting signal while driving said focal pointmoving means so that the first and second focal points pass through theinformation face.
 12. The apparatus of claim 11, wherein, upon a settingof the amplification factor of said amplifier, said focusing controlmeans is operated by detecting that an output signal from said amplifierreaches a prescribed value.
 13. The apparatus of claim 11, wherein saidinformation face detecting means detects that the focal point of thelight beam, suitable for the disk set in said optical disk apparatus, isnear the information face on the basis of a ratio of a low frequencysignal level of the output signal from said reflected light detectingmeans to an information reproducing signal level of the output signal.14. The apparatus according to one of claims 1 and 6, wherein thediscrimination of the disk set in said optical disk apparatus by saiddiscriminating means is performed after the focal point passes throughthe information face twice.
 15. The apparatus according to any of claims1 and 6, wherein the focal point is slightly moved in the directionperpendicular to a track on the disk during a period of time when thefocal point is passed through the information face, by controlling saidfocal point moving means.
 16. The apparatus according to any of claims 1and 6, wherein the moving speed of the focal point is reduced bycontrolling the focal point moving means when an output value from saidreflected light detecting means exceeds a prescribed value.